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Title: Outlines of dairy bacteriology

A concise manual for the use of

students in dairying

Author: H. L. Russell

E. G. Hastings

Release Date: May 14, 2010 [EBook

#32367]

Language: English

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EBOOK OUTLINES OF DAIRY BACTERIOLOGY ***

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OUTLINES OFDAIRY

BACTERIOLOGY

A CONCISEMANUAL FOR THE

USE OFSTUDENTS IN

DAIRYING

BY

H. L. RUSSELL

DEAN OF THE COLLEGE OF

AGRICULTURE

AND

E. G. HASTINGS

PROFESSOR OF AGRICULTURAL

BACTERIOLOGY

TENTH EDITION

MADISON, WISCONSIN

H. L. RUSSELL1914

COPYRIGHT 1914BY

H. L. RUSSELL AND E. G. HASTINGS

PREFACE TO THETENTH EDITION.

This text was originally the outgrowthof a series of lectures on the subject ofdairy bacteriology to practical studentsin the winter Dairy Course in theUniversity of Wisconsin. Theimportance of bacteriology in dairyprocesses has now come to be sowidely recognized that no student ofdairying regards his training ascomplete until he has had thefundamental principles of this subject.

The aim of this volume is not to

furnish an exhaustive treatise of thesubject, but an outline and sufficientdetail to enable the general student ofdairying to obtain as comprehensive anidea of the bacteria and their effects onmilk and other dairy products as maybe possible without the aid oflaboratory practice. When possible thedairy student is urged to secure alaboratory knowledge of theseorganisms, but lacking this, the studentand general reader should secure ageneral survey of the field ofbacteriology in relation to dairying.

In this, the tenth edition, the effort hasbeen made to include all of the recentdevelopments of the subject. Especiallyis this true in regard to the subject of

market milk, a phase of dairying thathas gained greatly in importance in thelast few years. The changes in themethods of handling market milk havebeen marked. The results of thesechanges in influencing the quality ofmilk offered to the consumer are fullydiscussed.

H. L. R.E. G. H.

CONTENTS

Structure,Growth andDistribution ofBacteria 7Methods ofStudyingBacteria 20Contaminationof Milk 28Infection ofMilk withPathogenicBacteria 62

Fermentationsof Milk 82Preservationof Milk 113Bacteria andButter Making 136Bacteria andCheeseMaking 161Bacteria inMarket Milk 189

CHAPTER I.

STRUCTURE, GROWTHAND DISTRIBUTION.

Relation of bacteriology to dairying.The arts which have been developed bymankind have been the outgrowth ofexperience. Man first learned by doing,how to perform these various activities,and a scientific knowledge of theunderlying principles which governthese processes was later developed.

The art of dairying has been practicedfrom time immemorial, but a correct

understanding of the fundamentalprinciples on which the practice ofdairying rests is of recent origin. Inworking out these principles, chemistryhas been of great service, but in lateryears, bacteriology has also been mostsuccessfully applied to the problems ofmodern dairying. Indeed, it may besaid that the science of dairying, asrelated to the problems of dairymanufacture is, in large degree,dependent upon an understanding ofbacteriological principles. It istherefore essential that the student ofdairying, even though he is concernedin large measure with the practicalaspects of the subject, should acquireas complete an understanding of these

principles as possible.

While bacteriology is concernedprimarily with the activities of thosemicroscopic forms of plant life knownas the bacteria, yet the generalprinciples governing the life of thisparticular class of organisms aresufficiently similar to those governingthe molds and other types ofmicroscopic life that affect milk and itsproducts to make it possible to includeall of these types in a generalconsideration of the subject.

Nature of bacteria. The vegetablekingdom to which the bacteria belongconsists of plants of the most varyingsize and nature. Those of most

common acquaintance are the greenplants varying in size from those notvisible to the naked eye to the largesttrees. Another class of plants known asfungi or fungous plants do not containchlorophyll, the green coloring matter,but are usually colorless and, as a rule,of small size; among them are includedsuch forms as the mushrooms, smuts,rusts and mildews, as well as the moldsand yeasts. The bacteria are closelyallied to this latter class. When firstdiscovered they were thought to beanimals because of the ability of someforms to move about in liquids.

The bacteria, like other kinds of livingorganisms, possess a definite form andshape. They are the simplest in

structure of all the plants, theindividual organism consisting of asingle cell. The larger and more highlyorganized forms of life are made up ofmany microscopic cells, and the life ofthe individual consists of the work ofall the cells. The bacteria are verycomparable to the single cells of thehigher plants and animals, but in thecase of the bacteria the single cell isable to exist apart from all other cellsand to carry out all of its life processesincluding reproduction.

Forms of bacteria. With themulticellular organisms much variationin form is possible, but with thesesingle-celled organisms the possiblevariation in form is greatly limited.

Three well marked types occur amongthe bacteria: the round or coccus form(plural cocci); the rod-shaped orbacillus (plural bacilli); and the twistedor spirillum type (plural spirilla). Mostorganisms of special significance indairying belong to the coccus orbacillus group.

Size of bacteria. The bacteria, as aclass, are among the smallest of livingobjects. None of them are individuallyvisible to the naked eye, and they canbe so seen only when clumps or massesare formed in the process of growth.

FIG. 1.—FORMS OF BACTERIA.

A, coccus; B, bacillus; C, spirillum.

While there is considerable relativevariation in size, yet in actualdimensions, this difference is so smallas to make careful microscopicdeterminations necessary. An averagediameter may be taken as about onethirty-thousandth of an inch, while thelength varies naturally several fold,depending upon whether the type underobservation is a coccus or a bacillus.

It is very difficult to conceive of theminuteness of the bacteria; thefollowing may give some idea of theirsize. In a drop of cream ready forchurning may be found as many as

10,000,000 and in a piece of freshcheese as large as a cherry there maybe as many living bacteria as there arepeople on our earth. While the bacteriaare very minute, the effect which theyexert in milk and other dairy productsis great on account of their enormousnumbers.

Manner of growth. The cells of whichall plants and animals consist increasein numbers by the division of each cellinto two cells through the formation ofa division wall across the cell. The newcells divide and the plant or animalcontinues to grow. The same celldivision occurs in the bacteria but sincethe bacteria are single celled, divisionof the cells means an increase in

numbers rather than growth as in thehigher forms of life.

FIG. 2.—DIVISION OF BACTERIA.

The bacteria increase in numbers bythe division of each cell into two

cells. (After Novy.)

In the case of those bacteria that have agreater length than diameter, the newwall is formed at right angles to thelong axis of the cell. As soon as thedivision is complete each cell is acomplete individual, capable ofcarrying on all of its life processes. Thecells may, however, cohere and thus

form distinctive groupings that mayserve to identify certain types. Some ofthe cocci form long chains and the termstreptococcus is applied to such. Othergroupings may be similar to a bale oftwine or they may be massed inclusters with no regularitydistinguishable.

Spores. Just as ordinary plants formresistant structures, known as seeds,capable of retaining vitality underconditions unfavorable for growththereby perpetuating the species, sowith certain of the bacteria, definitestructures, known as spores, that areanalogous in some respects to the seedsof the higher plants, are producedwithin the mother cell. The spores are

exceedingly resistant to the influenceof an unfavorable environment, such asheat, cold, drying, and even chemicalagents. It is this property of the sporeswhich makes it so difficult to destroythe bacterial life in the process ofsterilizing milk. The property of spore-formation is fortunately confined to acomparatively small number ofdifferent species of bacilli.

Movement. Many of the bacteria areprovided with vibratory organs oflocomotion, known as cilia (singularcilium) which are variously distributedon the surface of the cell. By themovement of these relatively long,thread-like appendages the individualcell is able to move in liquids. It must

be remembered, when these movingcells are observed under themicroscope, that their apparent rate ofmovement is magnified relatively asmuch as their size.

Conditions for growth. All kinds ofliving things need certain conditionsfor growth such as food, moisture, airand a favorable temperature. Thebacteria prefer as food such organicmatter as milk, meat, and vegetableinfusions. Those living on dead organicmatter are known as saprophytes, whilethose which are capable of thriving inthe tissues of the living plant or animalare known as parasites. Certain of theparasitic forms are capable of causingdisease in plants and animals. In the

first group are embraced most of thebacteria that are able to develop inmilk or its products, such as thoseforms concerned in the spoiling of milkor its fermentation. It is true that milkmay contain disease-producing bacteriacoming either from a diseased animalor from a diseased human being. It isalso true that some of such harmfulforms are able to grow in milk, such asthe organisms causing typhoid feverand diphtheria.

Food. The bacteria like all other plantsmust have their food in solution.Where they apparently live on solids,such as meats, fruits, etc., they dissolvethe food substances before utilizing thesame. If the solutions are highly

concentrated, as in the case of syrups,preserves and condensed milk, thebacteria cannot readily grow, althoughall of the necessary food ingredientsare present. When such concentratedsolutions are diluted, bacterial growthwill take place and the solutions willspoil.

FIG. 3.—PHOTOMICROGRAPH OF LACTIC

ACID BACTERIA.

Each cell is an individual organism,magnified 1250 diameters.

Generally speaking the bacteria grow

best in a neutral or slightly alkalinesolution rather than in acid liquids.

Temperature. One of the mostimportant conditions influencing therate of growth of bacteria is thetemperature. Each form has a minimumtemperature below which growth cannot take place; also a maximum abovewhich growth is again impossible. Forthe majority of species the minimumtemperature ranges from 40 to 45° F.the maximum from 105 to 110° F.Growth takes place most rapidly at theoptimum temperature, which, for eachspecies, lies close to the maximumtemperature at which growth can occur.Most of the bacteria of importance inthe dairy grow well at from 70 to 100°

F.

There are forms that can grow belowthe freezing point of water when theyare in solutions that do not freeze atthis temperature. There are still otherbacteria that can grow at 140° F. atemperature that is quickly fatal tomost forms. These are of importance inthe dairy since they limit thetemperatures at which milk can bestored for long periods of time.

Air supply. Living organisms, bothplant and animal, require air or oxygenfor the combustion of their food andfor the production of energy. Mostbacteria use, as do the green plants andanimals, the free oxygen of the air for

their respiration. Such organisms arecalled aerobic or air-living. A muchsmaller group possess the power oftaking oxygen from organiccompounds such as sugar and the likeand therefore are able to live underconditions where air is excluded. Theseare called anaerobic bacteria. A largenumber of bacteria are able to liveeither in the presence or in the absenceof free oxygen. Most of the bacteria ofimportance in the dairy are of thisnature.

Rate of growth. When there is anabundant supply of food and when thetemperature conditions are favorable,the bacteria increase in numbers withastounding rapidity. It has been

determined by actual experiment thatthe process of cell division underfavorable conditions takes place in afew moments. Barber has shown thatone of the forms of bacteria constantlyfound in milk will divide in 17 minutesat 98° F. and that a single organismkept at this temperature for ten hourswould increase to 1,240,000,000. If thetemperature is reduced to 50° F., thetime required for division is increasedto several hours. The explanation forthe rapid spoiling of milk that is notwell cooled is thus apparent. The initialrapid rate of increase cannot bemaintained for any length of time asthe conditions become more and moreunfavorable as growth continues, due

to the accumulation of the by-productsof the cell activity. Thus, the growth ofacid-forming organisms in milkbecomes checked by the formation ofacid from the fermentation of thesugar.

Detrimental effect of externalconditions. Environmental conditionsof a detrimental character areconstantly at work tending to repressthe activity of bacteria or to destroythem. These act more readily on thevegetating cells than on the moreresistant spores. It is of the utmostimportance that those engaged in dairywork be familiar with theseantagonistic forces since it isconstantly necessary to repress or to

kill outright the bacteria in milk andother dairy products. In many lines ofdairy work it is likewise important tobe familiar with the conditionsfavorable for bacterial growth.

Effect of cold. While it is true thatchilling largely prevents fermentativeaction, and actual freezing stops allgrowth processes, still it does notfollow that exposure to lowtemperatures will effectually destroythe vitality of bacteria, even in thegrowing condition. Numerous non-spore-bearing species remain alive inice for a prolonged period, andexperiments with liquid air show thateven a temperature of-310° F.maintained for hours does not kill all

exposed cells.

Effect of heat. High temperatures, onthe other hand, will destroy any formof life, whether in the vegetative orlatent spore stage. The temperature atwhich the vitality of the cell is lost isknown as the thermal death point. Thislimit is dependent not only upon thenature of the organism, but upon thetime of exposure and the condition inwhich the heat is applied. In a moistatmosphere, the penetrating power ofheat is great, consequently cell deathoccurs at a lower temperature than in adry atmosphere. An increase in time ofexposure lowers the temperature pointat which death occurs.

For growing organisms, the thermaldeath point of most species rangesfrom 130° to 140° F. for ten minutes.When spores are present, resistance isgreatly increased, some forms beingable to withstand steam at 212° F. fromone to three hours. In the sterilizationof milk, it is often necessary to heat forseveral hours, where a single exposureis made, to destroy the resistant spores,that seem to be more abundant undersummer than winter conditions. Steamunder pressure is a much moreeffective agent, as the temperature isthus raised considerably beyond 212°F. An exposure of twenty minutes, at atemperature of 230° to 240° F. will killall spores. Where heat is used in a dry

state, it is much less effective, a bakingtemperature of 260° to 300° F. for anhour being necessary to kill spores.This condition is of the utmostimportance in the destruction ofbacteria in the dairy and creamery.

Effect of drying. The spore-bearingbacteria withstand effects ofdesiccation without serious injury, andmany of the non-spore-producing typesretain their vitality for some months.The bacteria found in the air arepractically all derived from the soil,and exist in the air in a dried condition,in which they are able to remain alivefor considerable periods of time. In adried condition, active cell growth isnot possible, but when other

conditions, such as moisture and foodsupply are present, resumption ofgrowth quickly begins. This property isalso of importance in the dairy as in thepreparation of dry starters forcreameries and cheese factories.

Effect of light. Bright sunlight exerts amarkedly injurious effect on bacteriallife, both in a spore and in a growingcondition. Where the direct sunlightstrikes, more or less completedisinfection results in the course of afew hours, the effect being produced bythe chemical or violet rays, and not bythe heat or red rays of the spectrum.This action, however, does notpenetrate opaque objects, and istherefore confined to the surface. In

diffused light, the effect is muchlessened, although it is exerted to someextent. Sunlight exerts a beneficialeffect on the general health and well-being of animal life, and is a matter ofimportance to be taken intoconsideration in the erection ofbuildings for animals as well as forpeople.

Effect of chemicals. A great manychemical substances exert a more orless powerful toxic action on variouskinds of life. Many of these are of greatservice in destroying bacteria orholding them in check. Those that aretoxic and result in the death of the cellare known as disinfectants; those thatmerely inhibit, or retard growth are

known as antiseptics. All disinfectantsmust of necessity be antiseptic in theiraction, but not all antiseptics aredisinfectants, even when used in largeamounts. Disinfectants have no placein dairy work, except to destroydisease-producing bacteria, or topreserve milk for analytical purposes.The so-called chemical preservativesused to "keep" milk depend for theireffect on the inhibition of bacterialgrowth. In this country, most statesprohibit the use of these substances inmilk. Their only function in the dairyshould be to check fermentative andputrefactive processes outside of milkand so keep the air free from taints.

Products of growth. All bacteria, as a

result of their growth in foodsubstances, form more or lesscharacteristic compounds that areknown as by-products. The changesbrought about are those ofdecomposition and are collectivelyknown as fermentations; they arecharacterized by the production of alarge amount of by-products as theresult of the development of arelatively small amount of cell life.The souring of milk, the rotting ofeggs, the spoiling of meats, the makingof vinegar from cider are examples offermentations caused by differentbacteria.

If the substances decomposed containbut little sugar, as do animal tissues,

the conditions are favorable for thegrowth of the putrefactive bacteria, andfoul-smelling gases are formed. Whensugars are present, as in milk, theenvironmental conditions are mostfavorable for the acid-forming bacteriathat do not as a rule produce offensiveodors.

Many of the bacteria form substancesknown as enzymes which are able toproduce certain decomposition changesin the absence of the living cells, and itis by virtue of these enzymes that theorganisms are able to break down suchenormous quantities of organic matter.Most of these enzymes react towardheat, cold, and chemical poisons in amanner quite similar to the living cells.

In one respect, they are readilydifferentiated, and that is, thatpractically all of them are capable ofproducing their characteristic chemicaltransformations under conditionswhere the activity of the cell is whollysuspended as in a saturated ether orchloroform atmosphere. Theproduction of enzymes is not confinedto bacteria, but they are foundthroughout the animal and plant world,especially in those processes that areconcerned in digestion. Rennet, used incheese making, is an example of ananimal enzyme.

Distribution of bacteria. As bacteriapossess greater powers of resistancethan almost any other form of life, they

are found very widely distributed overthe surface of the earth. In soil they areabundant, because of the fact that all ofthe conditions necessary for growth arehere best satisfied. They are, however,distributed with reference to the layersof the soil; the soil proper, i.e., thatturned over by the plow, is extremelyrich in them on account of theabundance of organic matter. But at thedepth of a few feet they decreaserapidly in numbers, and in the deeperlayers, from six to ten feet, or more,they are normally not present, becauseof the lack of proper food supply andoxygen. The fertility of the soil isclosely associated with their presence.

The bacteria are found in the air

because of their development in thesoil below. They are unable to groweven in a moist atmosphere, but are soreadily dislodged by wind currentsfrom the soil that over land areas thelower strata of the air always containthem. They are more numerous insummer than in winter; city aircontains larger numbers than countryair. Wherever dried fecal matter ispresent, as in barns, the air containsmany forms.

Water generally contains enoughorganic matter in solution, so thatcertain types of bacterial life findfavorable growth conditions. Water incontact with the soil surface takes upmany impurities, and is of necessity

rich in bacteria. As the rain waterpercolates into the soil, it loses itsgerm content, so that the normalground water, like the deeper soillayers, contains practically no bacteriallife. Springs, therefore, are relativelydeficient in germ life, except as theybecome contaminated with soilorganisms, as the water issues from theground. Wells vary in their germcontent, depending upon manner ofconstruction, ease of contamination atsurface, etc. Wells are too frequentlyinsufficiently protected from surfaceleachings, and consequently maycontain all kinds of organisms found inthe surface soil. Typhoid fever is veryfrequently disseminated in this way, as

is cholera and a number of animalmaladies.

While the inner tissues of healthyanimals are free from bacteria, thenatural passages, as the respiratory anddigestive tracts, being in more directcontact with the exterior, becomereadily infected. This is particularlytrue with reference to the intestinaltract, and in the undigested residue ofthe food, bacterial activity is at amaximum. The result is that fecalmatter of all kinds contains enormousnumbers of organisms so that thepollution of any food medium, such asmilk, with such material is sure tointroduce elements that seriously affectits quality.

CHAPTER II.

METHODS OF STUDYINGBACTERIA.

Necessity of artificial cultivation. Thebacteria are so extremely small, that itis impossible to study individual germsseparately without the aid of powerfulmicroscopes. Little advance was madein the knowledge of these lower formsof plant life until the introduction ofculture methods, whereby a singleorganism could be cultivated, and theprogeny of this cell increased to such

an extent in a short course of time thatthe resulting mass of cells would bevisible to the unaided eye. This is doneby growing the bacteria on variouskinds of nutrient media that areprepared for the purpose, but inasmuchas bacteria are so universallydistributed, it becomes an impossibilityto cultivate any special form alone,unless the medium in which they aregrown is first freed from all pre-existing forms of germ life.

Food materials. Many kinds of foodsubstances are used for the cultivationof bacteria in the laboratory. In fact,bacteria will grow on almost anyorganic substance, whether it is solid orliquid, provided the other essential

conditions of growth are furnished. Thefood substances that are used forculture purposes are divided into twoclasses,—solids and liquids.

Solid culture media may be eitherpermanently solid, like potatoes andcoagulated egg, or they may retaintheir solid properties only at certaintemperatures, like gelatin or agar. Thelatter two, which were devised byRobert Koch, are of utmost importancein bacteriological research, for theiruse permits the separation of thedifferent forms of bacteria that mayhappen to be in any mixture. Gelatin isadvantageously used, because themajority of bacteria present widerdifferences, due to growth upon this

medium, than upon any other. Itremains solid at ordinary temperatures,becoming liquid at about 80° F. Agar, agelatinous product derived from aJapanese seaweed, has a much highermelting point, and is used especiallywith those organisms whose optimumtemperature for growth is above themelting point of gelatin.

Besides these solid culture media,different liquid substances areextensively used, such as beef broth,milk and infusions of various vegetableand animal tissues. Skim milk is ofespecial value in studying the milkbacteria, and may be used in its naturalcondition, or a few drops of litmussolution may be added, in order to

detect any change in its chemicalreaction due to the bacteria.

Sterilization. The various ingredientsthat are used in the preparation ofculture media are not free from micro-organisms, hence the media wouldsoon spoil if they were not destroyed,and the media subsequently protectedfrom contamination from the air, etc.The process of rendering the mediafree from living micro-organisms isknown as sterilization. It may beaccomplished in a number of ways, butmost often is done by the use of heat.For culture material, which is alwaysorganic in character, moist heat isemployed. The various culture media,in appropriate containers, are subjected

to a thorough steaming in a steamcooker. This destroys all of thevegetating cells but not the resistantspores that may be present. The mediaare then stored, for twenty-four hours,at temperatures favorable for thegermination of the spores and are thenagain heated. Three such applicationson successive days are usuallysufficient to free the media from allliving germs, since between the heatingperiods the spores germinate and theresulting vegetative cells are moreeasily destroyed. The sterile media willkeep for an indefinite period in a moistplace.

The media are usually placed in glasscontainers which may be sterilized

before use by heating them in an oven,it being possible to thus secure a muchhigher temperature than with streamingsteam. All glass or metal articles maybe sterilized by the use of dry heat butfor organic media, to avoid burning,moist heat must be used.

All kinds of materials may be sterilizedby treatment with steam underpressure. An exposure for a fewmoments at 250° F., a temperatureattained with 15 pounds steampressure, will destroy all kinds ofbacteria and their spores. This methodof sterilization is used in the canning ofmeats and vegetables and in thepreparation of evaporated milk. Toavoid contamination of the media after

sterilization, the flasks and tubes are,after being filled, stoppered with plugsof cotton-wool, which effectually filterout all bacteria and mold spores fromthe air, and yet allow the air to passfreely in and out of the containers.

Methods of determining the numberof bacteria. The method ofdetermining the number and kinds ofbacteria in any substance can beillustrated by the process as applied tomilk. For this purpose the method ofprocedure is as follows: Sterile gelatinin glass tubes is melted and then cooleduntil it is barely warm. To this meltedgelatin a definite quantity of milk isadded. The medium is gently shaken,so as to thoroughly mix the milk and

gelatine, and the mixture then pouredinto a sterile, flat, glass dish, andquickly covered, where it is allowed tocool until the gelatin hardens. After theculture plate has been left for twenty-four to thirty-six hours at the propertemperature, tiny spots will begin toappear on the surface, or in the depth ofthe culture-medium. These spots arecalled colonies, and are composed ofan almost infinite number of individualcells, the result of the continued growthof a single organism that was in thedrop of milk and which was firmly heldin place when the gelatin solidified.The number of these coloniesrepresents approximately the numberof living bacteria that were present in

the amount of milk added to the tube ofgelatin. If the plate is not too thicklysown with the bacteria, the colonieswill continue to grow and increase insize, and as they do, minute differenceswill begin to appear. These differencesmay be in the color, the contour, andthe texture of the colony, or the mannerin which it acts toward gelatin.

FIG. 4.—PLATE CULTURE.

Each of the dots is a colony that hasbeen formed by the growth of anorganism embedded in the solid

culture-medium. By counting thecolonies, the number of living

bacteria in the amount of milk addedto the culture is determined.

In order to make sure that the numberof colonies is not so numerous as toprevent counting and further study oftheir characteristics, a series of platecultures is usually made in whichvarying amounts of milk are added tothe tubes of gelatine. This is attainedby adding a definite amount of the milkor other substance to be examined to ameasured amount of sterile water, e.g.,one cubic centimeter of milk to ninety-nine cubic centimeters of water. Onecubic centimeter of this mixture maybe used for the inoculation of the plateculture. This dilution may be carried onto any desired extent; in the

examination of many dairy products, itis necessary to use very minutequantities of material, often only oneone-millionth of a cubic centimeter.

To study further the peculiarities of thedifferent bacteria, small portions of theindividual colonies are transferred totubes of sterile culture-media. In orderto do this the colony is touched with apiece of platinum wire; the minuteamount of growth that adheres to thewire is sufficient to seed the tube offresh culture-medium. The inoculatingneedle must always be sterilized beforeuse by passing it through a gas flame.

A culture thus obtained is called a pureculture since it contains but a single

kind of an organism, as the colony isthe result of the growth of a single cell.These cultures then serve as a basis forcontinued study, and must be plantedand grown upon the different kinds ofmedia that are obtainable. In this waythe slightest variations in the growth ofdifferent forms are detected, and thepeculiar characteristics are determined,so that the student is able to recognizethis form when he meets it again.

FIG. 5.—DIFFERENT KINDS OF BACTERIA

GROWING IN GELATIN.

A, meager growth, no liquefaction orsurface growth; B, profuse surface

growth, radiating filaments from thegrowth below the surface; C, a rapidliquefying form; D, a gas producer

that grows equally well in the

presence or absence of air; E, formthat grows only in the absence of air,

an anaerob.

These culture methods are of essentialimportance in bacteriology, as it is theonly way in which it is possible tosecure a quantity of germs in a purestate.

The microscope in bacterialinvestigations. In order to verify thepurity of the cultures, the microscopeis in constant demand throughout allthe different stages of the isolatingprocess. For this purpose it is essentialthat the instrument used shall be one ofhigh magnifying powers (600 to 800diameters), combined with sharp

definition.

The microscopical examination of anygerm is quite as essential as thedetermination of culturecharacteristics, in fact, the two must gohand in hand. The examination revealsnot only the form and size of theindividual germs but the manner inwhich they are united with each other,as well as any peculiarities ofmovement that they may possess.

In carrying out the microscopical partof the work, not only is the organismexamined in a living condition, butcolored preparations are made by usingsolutions of anilin dyes as stainingagents. These are of great service in

bringing out almost imperceptibledifferences. The art of staining hasbeen carried to the highest degree ofperfection in bacteriology, especiallyin the detection of germs that are foundin diseased tissues in the animal orhuman body.

In studying the peculiarities of anyspecial organism, not only is itnecessary that these cultural andmicroscopical characters should beclosely observed, but specialexperiments must be made in differentways, in order to determine any specialproperties that the germ may possess.Thus, the ability of any form to act as afermentative organism can be tested byfermentation experiments; the property

of causing disease, studied by theinoculation of pure cultures intoexperimental animals, like rabbits,guinea pigs and white mice.

The methods of the bacteriologist inhis laboratory are in their effect notdissimilar to those which the farmeremploys in securing his crop of pure-bred grain. The laboratory farmer killsthe weed seeds in his culture field bythe application of heat. His field, whichis embraced in his culture dish, hasbeen fertilized and prepared by theaddition of certain favorableingredients. When he has garnered hiscrop, he maintains its purity by keepinghis selected seed, the pure culture, freefrom all contamination. The dairyman,

even though he may not expect to carryon the detailed operations of thelaboratory, will understand the reasonfor the directions which he is oftenrequired to follow much better if heknows how the simple operations of thelaboratory are carried out. For a fullerknowledge of these matters, the readeris referred to the special texts onbacteriology.

CHAPTER III.

CONTAMINATION OFMILK.

Spoiling of milk. Materials of animalorigin are peculiarly prone to undergochanges, rendering them unfit for use,and of these, milk is exceedinglysusceptible to such changes. This is dueto the fact that the composition of milkis especially adapted to bacterialgrowth, and that the opportunity forentrance of such organisms is likewisesuch as to permit of abundant

contamination. The consequence is thatmilk readily undergoes fermentativechanges, due to the development of oneor another type of micro-organism.

Milk, a suitable bacterial food. Whilemilk is designed by nature for thenourishment of mammalian life, it is,curiously enough, equally well adaptedto the growth of these lowest forms ofvegetable life. The nutritive substancesrequired by bacteria are heresufficiently dilute to make possiblerapid growth.

Milk also contains all the necessarychemical substances to make a suitablebacterial food supply. Of thenitrogenous compounds, albumen is in

a readily assimilable form. Casein, theprincipal nitrogenous constituent ofmilk, exists in an insoluble condition,and cannot be directly utilized, until itis acted upon by digesting enzymes.The fat in milk does not readilydecompose, and while there are a fewbacteria capable of splitting thissubstance, the majority of organismsare unable to utilize it. Milk sugar, onthe other hand, is an excellent food formost species.

FIG. 6.—FAT GLOBULES AND BACTERIA.

Note the relative size of the fatglobules of milk and the lactic acid

bacteria.

Sources of contamination. Inasmuch

as milk is especially exposed to theinroads of bacterial growth, andbecause of the fact that much of thecontamination can easily be prevented,it is highly important that the milkproducer and dealer should bethoroughly cognizant of the varioussources of contamination. The differentfactors concerned in contaminationmay be grouped as follows: the interiorof the udder; utensils, including allapparatus with which the milk isbrought in contact subsequent towithdrawal from the animal; infectioncoming from the animal herself, fromthe milker, and the surrounding air.

Condition of milk when secreted.Immediately after withdrawal from the

udder, milk always contains bacteria,yet in the secreting cells of the udder ofa healthy cow, germ life does not seemto be present. Only when the gland isdiseased are bacteria found in anyabundance. In the passage of the milkfrom the secreting cells to the outside,it receives its first infection, so thatwhen drawn from the animal itgenerally contains a considerablenumber of organisms.

A study of the structure of the uddershows the manner in which suchinfection occurs.

Structure of the udder. The udder iscomposed of secreting tissue (glandcells) that is supported by fibrous

connective tissue. The milk iselaborated in these cells and isdischarged into microscopic cavities,from whence it flows through thenumerous channels (milk sinuses) thatramify through the substance of theudder, until finally it is conveyed intothe milk cistern, a common receptacleholding about one half pint that islocated just above the teat. This cavityis connected with the outside by adirect opening (milk duct) through theteat. During the process of milking, themilk is elaborated rapidly in the glandcells, and their contents upon ruptureof the milk cells, flow down into thecistern. The normal contraction of themuscles at the lower opening of the

outer duct prevents the milk frompassing out except when pressure isapplied, as in milking. The inner wallsof the milk duct and cistern are alwaysmore or less moist, and thereforeafford a suitable place for bacteria todevelop, if infection once occurs, andconditions are favorable for growth.

Manner of invasion. Two possiblesources of invasion of the udder bybacteria may exist. If bacteria arepresent in the circulating blood, thereis the possibility of organisms passingdirectly through the tissues into themilk-secreting cells. The otheralternative is the possible directcontamination from the outside byorganisms passing up through the milk

duct, and so spreading through the openchannels in the udder.

FIG. 7.—SECTIONAL VIEW OF UDDER.

Teat with milk duct connecting theexterior with the milk cistern. Milk

sinuses which conduct the milk fromthe secreting tissue to the milk

cistern. (After Moore & Ward.)

Number of bacteria in fore-milk. If abacteriological examination is made ofthe milk drawn from each teat atdifferent periods during the milkingprocess, it will be found that the fore-m i l k , i.e., the first few streams,contains, as a rule, many moreorganisms per cubic centimeter thanthat removed later. Not infrequentlythousands of organisms per cubiccentimeter may be found in the firststreams while the middle milk, or

strippings, will contain much smallernumbers.

Distribution and nature of bacteriain udder. If the udder itself is carefullyexamined as to its bacterial content, itappears that the majority of organismsfound is confined to the lower portionof this organ, in the teat, milk-cisternand large milk-ducts; while bacteriaoccur in contact with the secretingtissue, they are relatively lessabundant. This would seem to indicatethat the more probable mode ofinfection is through the open teat.

While there is no constant type ofbacteria found in the fore-milk, yet it isnoteworthy that nearly all observers

agree that the organisms mostcommonly found are not usually theacid-producing, or gas-generating type,so abundant on the skin or hairy coat ofthe udder and which predominate inordinary milks. Coccus forms,belonging to both liquefying and non-liquefying types are most generallypresent. Many of these produce acidslowly and in small quantities.

The bacteria coming from the interiorof the udder are of small practicalsignificance since they do not growrapidly at the temperatures at whichmilk is stored. If the milk is protectedfrom contamination from othersources, the bacteria from the udderwill ultimately cause it to spoil, but

under ordinary conditions other formsare present in such greater numbers,and grow so much more rapidly inmilk, that the udder forms have smallopportunity to exert any effect.

It is interesting to note that the bacteriafound in the udder are similar to thosethat seem to be most abundant in suchglandular tissues as the liver andspleen. This fact increases theprobability that these comparativelyinert coccus forms of the udder mayoriginate directly from the bloodstream. The organisms that normallyare found in the udder exert no harmfuleffects on the gland. It might bethought that due to the presence ofabundant food and a favorable

temperature that growth would beabundant, but such is not the case. Attimes the udder may be invaded byforms that are not held in check by thenatural factors and an inflammation ofthe udder is likely to result.

Germicidal property of milk. It hasbeen claimed that freshly drawn milk,like other body fluids, possessesgermicidal properties, i.e., the power ofdestroying bacteria with which it maybe brought in contact. If milk iscarefully examined bacteriologically,hour by hour, after it is withdrawnfrom the udder, it will generally befound that there is at first not only noincrease in number of organismsduring a longer or shorter period when

it is kept at temperatures varying from40° to 70° F., but that an actualreduction not infrequently takes place.When cultures of bacteria, such as B.prodigiosus, a red organism, lactic acidorganisms, and even the yellow,liquefying coccus, so commonly foundin the fore-milk, are artificiallyintroduced into the udder, it has beenfound that no growth occurs and that inthe course of a few days the introducedorganisms actually disappear. Whetherthis failure to colonize can be regardedas evidence of a germicidal property ornot is questionable. In fact, thisquestion is a matter of but littlepractical importance in the handling ofmilk since, under the best of

conditions, the keeping quality of themilk is not materially enhanced. It maybe of importance in inhibiting growthin the udder.

Rejection of fore-milk. The fact thatthe fore-milk contains per cubiccentimeter so much more germ lifethan the remainder of the milk has ledsome to advocate its rejection when asanitary milk supply is underconsideration. While from a purelyquantitative point of view, this custommay be considered advantageous, inpractice, however, it is hardly worthwhile since it is not at all certain thatthe rejection will have any effect on thekeeping quality or healthfulness ofmilk. This is especially true if the ends

of the teats are thoroughly cleanedbefore milking. It is true that the fore-milk is relatively deficient in fat sothat the loss of butter fat occasioned bythe rejection of the first few streams iscomparatively slight.

Contamination from utensils. One ofthe most important phases ofcontamination is that which comesfrom the utensils used to hold the milkfrom the time it is drawn until it isutilized. Not only is this importantbecause it is a leading factor in theinfection of milk, but because muchimprovement can be secured with butlittle trouble, and it is especiallynecessary that the dairy student shouldbe made familiar with the various

conditions that obtain. Pails and cansused to hold milk may be apparentlyclean to the eye, and yet contributematerially to the germ content of themilk placed in them. Not only doesmuch depend upon their condition, butit is equally important to take intoconsideration their manner ofconstruction. Dairy utensils should besimple in construction, rather thancomplex. They should be made so thatthey can be readily and easily cleaned,or otherwise the cleaning process is aptto be neglected.

Of first importance are those utensilsthat are used to collect the milk and inwhich it is handled while on the farm.The warm milk is first received in

pails, and unless these are scrupulouslycleaned, an important initialcontamination then occurs. Asordinarily washed, the process falls farshort of ridding the utensils of thebacterial life that is adherent to theinner surface of the pail. Then, too, allangles or crevices afford an excellenthiding place for bacteria, and it is veryimportant to see that all seams are wellsoldered. Round corners and anglesflushed with solder greatly facilitatethorough cleaning of utensils. Tinutensils are recognized as mostsatisfactory.

Shipping cans are likely to serve asgreater infecting agents than pails forthey are subject to more wear and tear

and are harder to clean. As long as thesurface is bright and smooth, it may beeasily cleaned, but large utensils, suchas cans, are likely to become dentedand rusty in spots on the inner side.The storage of milk in such utensilsresults in its rapid deterioration. Theaction of rennet has been found to begreatly retarded where milk comes incontact with a rusty iron surface. It isalso probable that some of theabnormal flavors in butter are due tothe action of acid cream on iron orcopper surfaces from which the tin hasbeen worn. It is equally important thatattention be paid to the care ofstrainers, coolers, and the smallutensils. Cloth strainers are more or

less of a hotbed for bacterial growth,for unless they are boiled, and thendried quickly and thoroughly, germgrowth will continue apace in them, aslong as they contain any moisture.

Milking machines and farmseparators. The introduction of thesespecial types of dairy machinery in thehandling of milk on the farm hasmaterially complicated the question ofthe care of milk. Both of these types ofapparatus are much more complicatedthan the usual milk utensil;consequently, the danger of imperfectcleaning is thereby increased. This isstill further accentuated by the fact thatcleansing of utensils on the farm cannever be done so well as at the factory

or milk depot where steam is available.The milking machine may be easilykept in a comparatively germ-freecondition, but unless this is done, itcontributes its quota of germ life to themilk.

The farm separator is more widely usedthan the milking machine and in actualpractice the grossest carelessnessprevails in the matter of its care.Frequently it is not taken apart andthoroughly cleansed, but is rinsed outby passing water through the machine.It is impossible by such a treatment toremove the slime that collects on thewall of the bowl; the machine remainsmoist and bacterial growth can go on.Such a machine represents a most

important source of contamination ofmilk and cream and it is probable thatthe widespread introduction of the handseparator has contributed more tolower the quality of cream delivered atthe factory than any other single factor.

Contamination from factory by-products. The custom of returningfactory by-products in the same set ofcans that is used to bring fresh milk isa prominent cause of bad milk. Wheyand skim milk are rich in bacterial life,and not infrequently are so handled asto become a foul, fermenting mass. Ifthe cans used to transport this materialare not scrupulously cleaned on thefarm, transfer of harmful bacteria tothe milk is made possible. In this way

the carelessness of a single patron maybe the means of seeding the wholefactory supply. This custom is not onlyliable to produce a poor quality ofmilk, but it is more or less of a menaceto all the patrons of a factory,inasmuch as the opportunity alwaysobtains that disease-producingorganisms may thus be introduced intothe supply. Not infrequently istuberculosis thus spread through themedium of factory by-products.

FIG. 8.—WHEY DISPOSAL.

Whey barrels at a Wisconsin Swisscheese factory. Each patron's share is

placed in a barrel which is sosituated that it is impossible to

empty it completely; thus it is notcleaned during the season.

The manufacture of Swiss cheesepresents a striking example of thedisregard which factory operators show

toward the employment ofbacteriological principles. In thesefactories, the custom is widelypracticed of apportioning the patrons'allotment of whey into individualbarrels which are supposed to beemptied each day. As these barrels are,however, rarely ever cleaned from thebeginning to the end of the season, theybecome very foul, and the whey placedin them from day to day highlypolluted. It is this material which istaken back to the farms in the same setof cans that is used for the fresh milk.When one recalls that the very besttype of milk is essential for the makingof a prime quality of Swiss cheese, andthat to secure such, the maker insists

that the patron bring the product to thefactory twice daily, the beforementioned practice appears somewhatinconsistent.

Treatment of factory by-products. Toovercome the danger of infecting milkfrom factory by-products with eitherundesirable fermentative organisms, ordisease-producing bacteria, the mostfeasible process is to destroy theseorganisms by the application of heat. InDenmark, some portions of Germany,and in some of the states in thiscountry, laws exist which require theheating of all skim milk before it isreturned to the farm. This is done bythe direct use of exhaust steam, orrunning the product through heaters.

The treatment of whey in cheesefactory practice is especially importantsince the warm whey must be storedfor a number of hours before it isreturned to the farms. Even under thebest of conditions the whey is certainto be in an advanced state offermentation when placed in the milkcans, and it only needs the infection ofthe whey tank with harmful bacteria tocause great loss on account of theinjury of the product by these bacteria.Among Canadian factories the customof heating the whey as it passes fromthe cheese vat to whey tank has beenintroduced, and where ever adopted hasbeen retained, because, it has resultedin such an improvement of the cheese

that the gain was much greater than thecost, which is estimated at not overfifty cents per ton of cheese. The wheyis heated not to exceed 155° F.; the hotwhey serves to scald the whey tank andas the mass of whey is usually quitelarge, it does not cool to a point wherebacterial growth can take place for anumber of hours. The whey is thusquite sweet when returned to the farmand has greater feeding value. Theheating also prevents the creaming ofthe whey in the tank and thus avoidsthe soiling of the cans with greasewhich is most difficult to remove.

Where compulsory legislation is inforce it is generally required that theseby-products be heated to a temperature

of at least 176° F. This is done so as todestroy effectually the organisms oftuberculosis, and especially to permitof the utilization of the so-calledStorch test,[1] which enables a personto determine quickly whether milk orwhey has been heated or not.

[1] Storch (40 Rept. Expt. Stat.,Copenhagen, 1898) has devised atest whereby it can be determinedwhether this treatment has beencarried out or not; milk contains asoluble enzyme known asperoxidase which has the propertyof decomposing hydrogen peroxid.If milk is heated to 176° F., (80° C.)or above, this enzyme is destroyed,so that the above reaction no longertakes place. If potassium iodide and

starch are added to unheated milkand the same treated with hydrogenperoxid, the decomposition of thelatter agent releases oxygen whichacts on the potassium salt, which inturn gives off free iodine that turnsthe starch blue.

Cleaning utensils. Various processesare applied to dairy utensils to cleansethem. In removing visible dirt andforeign matter, much of the bacteriallife is mechanically eliminated, butmost of the cleaning processes fail todestroy the germ life in these utensils.

In rinsing, washing, or even scalding,the water is not applied at a sufficientlyhigh temperature to destroy effectivelythe bacteria. These processes are

primarily used for the removal of dirtand other matter. To facilitate suchremoval, washing powders of variouskinds are frequently employed; someof these possess considerabledisinfecting action. All utensils aftercleansing should be thoroughly rinsedin clean, hot water. Even where nofurther treatment is given, a carefulcleaning may so reduce the germcontent on the inner surface of utensilas to render contamination therefromrelatively unimportant. Most of thecontamination in a well cleaned utensilcomes from the cracks and angles,which permit of the collection of thedirt. If these are properly attended to,thorough cleaning and rinsing alone

will accomplish much.

To exert an actual germ-destroyingeffect on the bacterial content of theutensil, resort must be had to boiling orsteaming. To treat utensils so as torender them wholly germ-free wouldbe impractical under ordinarycommercial conditions, as it wouldconsume too much time, although withproper apparatus, this process is notimpossible, but it is well within thelimits of practicability in factorytreatment to apply steam for a shortperiod of time. Where cans, pails andsuch utensils, are steamed for a minuteor so after being thoroughly cleaned,the germ content is greatly reduced. Ina series of tests by Harrison, the germ

content of a set of cans cleaned in anordinary way was 442,000 bacteria percubic centimeter in 100 cubiccentimeters of wash water; in a setwashed in tepid water and then scalded—the best farm practice—it was54,000 per cubic centimeter, while incans carefully washed and thensteamed for 5 minutes, it was reducedto 880 per cubic centimeter. It wouldnot be worth while to institutemeasures that would accomplish thedestruction of this small residualcontent.

The use of steam, therefore, is of greatservice in eliminating bacterial life inall utensils. In apparatus of at allcomplicated design, it is absolutely

necessary. Of course, ordinarily, steamcan be applied only at the factory, asthe farm does not usually affordfacilities for its easy generation. Thisfact has led in some cases to theadoption of the method of cleaning andsterilizing the cans at the factory ratherthan to await their arrival at the farm.This custom is most frequentlyfollowed in milk supply plants.

It is also very important in cleaningdairy utensils to see that they arerapidly and thoroughly dried afterbeing washed and steamed. As pointedout above, the short period of steamingthat can be followed in practice doesnot kill all the bacteria. If moisture isretained, conditions permit of the

growth of the undestroyed organisms.Tests made on glass milk bottlesshowed that considerable growthoccurred in the condensation watereven after quite thorough sterilization.Some of the devices used for thesterilization of such utensils as milkcans are so arranged that, after steamhas been introduced, hot air is passedinto the can until it is thoroughly dried.Other utensils such as cloth strainersbecome sources of contaminationunless the articles are thoroughly andquickly dried after cleaning.

In a general way, it may be said thatwhenever a utensil is so constructedand in such a condition that everyportion of its surface can be reached by

a cloth or a brush, it can be kept in asanitary condition. But whenever anyportion cannot be thus reached,whether it is an angle or a seam in apail or can, the interior of the separatorbowl, or in the pipes used forconducting milk, contamination iscertain to result from such places,unless extreme care is taken to destroythe bacteria therein by steaming.

Contamination from the animal. Inthe process of milking, the bacterialcontent of the milk is materiallyincreased. In part this comes from theutensils into which the milk is drawn,but the animal herself, the milker, aswell as the surrounding air, alsocontribute to a varying extent. Of these

factors, the one fraught by far with themost consequence, is the influence ofthe animal herself. It is a popular beliefthat the organisms found in milk arederived from the feed and water whichthe animal consumes, but under normalconditions, the bacteria consumed infood pass through the intestinal canaland do not appear in the circulation. Itmust not be assumed, however, that thecharacter of feed and water supply is ofno moment. Stock should be given pureand wholesome water and nodecomposed or spoiled food should beused.

The infection traceable directly to thecow is modified materially by theconditions under which the animal is

kept and the character of the feedconsumed. The nature of the fecalmatter is in part dependent upon thecharacter of the food. The morenitrogenous the ration fed, the softerare the fecal discharges, producing acondition which is more likely to soilthe coat of the animal unless care istaken. The same is true with animalskept on pasture in comparison withthose fed dry fodder.

Stall-fed animals, however, are morelikely to have their flanks fouled,unless special attention is paid to theremoval of the manure. All dairy stallsshould be provided with a manure dropwhich should be cleaned as frequentlyas circumstances will permit.

FIG. 9.—BACTERIA ON HAIRS.

Each colony on the hair representsone or more bacteria that were

adherent to the hair when it was

placed on the surface of the solidculture-medium.

The animal contributes materially tothe quota of germ life finding its wayinto the milk through the dislodgmentof dust and filth particles adhering toits hairy coat. The nature of this coat issuch as to favor the retention of theseparticles. Unless care is taken, theflanks and udder become polluted withfecal matter, which upon drying isdisplaced with every movement of theanimal. Every hair or dirt particle sodislodged and finding its way into themilk-pail adds its quota of organismsto the liquid. This can be readilydemonstrated by placing cow's hairs onthe moist surface of gelatin culture

plates. Almost invariably bacteria willbe found in considerable numbersadhering to such hairs, as is indicatedin Fig. 9.

Dirt particles are even richer in germlife. Not only is there the dislodgmentof hairs, epithelial scales, and massesof dirt and filth, but during the milkingprocess, as at all other times, everymotion of the animal is accompaniedby a shower of invisible particles, moreor less teeming with bacterial life. Allof this material contains organisms thatare more or less undesirable in milk.Bacteria concerned in gassyfermentations and those capable ofproducing obnoxious taints areparticularly common, so that this type

of pollution is especially undesirable inmilk.

Amount of dirt in milk. When oneremembers that the larger part of freshmanure is of such a nature that it doesnot appear as sediment, the presence ofevident filth in milk must bespeakcareless methods of handling.

The sediment or dirt test is used quiteextensively to ascertain the amount ofdirt milk may contain. By means of acotton filter, the insoluble residue isremoved and is made evident upon alayer of absorbent cotton. Milk thatwould show with difficulty anyevidence of dirt upon ordinaryexamination reveals such defects very

readily in this test.

Exclusion of dirt. It is better to keepbacteria out of milk, so far aspracticable, rather than to attempt toremove them after they have oncegained entrance. As is usual,prevention of trouble is much moreeasily accomplished than removing thedifficulty after it once occurs.

FIG. 10.—DIRT FROM MILK.

The dirt adherent to each of thefilters was obtained from one pint of

milk. The milks tested wereproduced on different farms.

Much reduction as to the amount ofdirt that finds its way into milk may beaccomplished by improved stable

environment. The fouling of the udderand flanks comes from wading in dirtywater, muddy yards, and fromimproper type of stalls. Barnyards areoften a disgrace through theaccumulation of manure and seepage.Cows wading in such mire cannot butaccumulate mud and filth to a materialdegree on the teats and udder. Greatercare as to drainage of the barnyard andthe paving of same with gravel,cinders, etc., will permit of its beingkept clean, and so prevent the foulingof animals. But more important thanthe yard is the stall which the animaloccupies in the stable. The essentialfeature is to have a stall of suchconstruction as to keep the animal out

of her own manure when she lies down.To accomplish this, it is necessary tohave a manure drop behind the stallproper so that the feces and urine arekept out of the bed of the stall as muchas possible.

FIG. 11.—THE MODEL STALL.

A stall of this type keeps the animalsclean, and thus aids greatly in

producing good milk.

Most of the stalls widely advertised inthe farm press seek to accomplish thisin one way or another, usually by somearrangement by which the cow isforced back when standing and drawnforward on lying down. In Fig. 11 atype of stall is illustrated thataccomplishes this most successfully;the essential feature being a 2×3-inchwood strip nailed to the stall floorimmediately in front of the hind feet ofthe animal when in a standing position.When the animal lies down, she crowdsforward to avoid lying on this strip, andthus is out of contact with the manure,except such as is carried onto thebedding by the hind feet. By the use of

this stall it is possible to keep theanimals free from all accumulations ofmanure.

Effort should be made to preventfouling of the animals rather than incleaning them after once soiled. It isvery evident that where the cattle cometo the milker with muddy udders, theywill not be so cleaned before milkingas to prevent a large amount of suchdirt from entering the milk. However,when all that can be done towardskeeping the cows clean has beenaccomplished, a small amount ofgrooming will greatly reduce thecontamination coming from them.

The kind of bedding used in the stalls

may have a marked influence on thecontamination coming from theanimal. If the straw is dusty, partiallyrotten and moldy, the bacteria andmolds adhere to the coat of the animaland are thus introduced into the milk.In the case of cattle on pasture, novisible evidences of dirt are usuallypresent but the hair is covered with thedust coming from the soil. There isvery good reason to believe that thequality of milk is influenced by thetype of pasture on which the cowsgraze, due to the difference in the typesof bacteria in the surface soil. The milkfrom animals on low land is morelikely to show undesirablefermentations than that from those

grazing on higher lands. This is not dueto the influence of the feed as is oftensupposed but rather to the dirt from thecoat of the animal.

Washing the udder. If a surface ismoist, dust and the adherent bacteriacannot be easily dislodged. The airover snow-covered mountains or overoceans is relatively free from bacteria.The udder and flanks of the animalscan be carded to remove the loose hairsand the evident dirt; the fine dust cannow be removed by wiping with a cleandamp cloth just before the milkingprocess. The actual washing and wipingof the udder and flanks still furtherreduces the contamination comingfrom the animal; experiments show a

reduction of fully three-fourths of totalcontamination. Clipping the udder andflanks also aids in keeping the animalclean.

It is often asserted that the treatment ofthe animals in these ways reduces theyield of milk. It is certain that such aneffect will persist for only a short timeand there is reason to believe thatgrooming increases the yield.

FIG. 12.—SANITARY MILK PAILS.

The small opening is very efficient inkeeping the dirt out of milk.

Sanitary milk pails. The entrance oforganisms into the milk can be greatlyreduced by lessening the area of themilk pail exposed to the dust shower.To accomplish this purpose a numberof so-called sanitary or hygienic milkpails have been devised. In some cases,

these are the regular type of pailprovided with a cover having a smallopening through which the milk isreceived. In other cases, a strainer isinterposed so as to remove moreeffectually the coarse particles. Whilepails of this type are successful in theremoval of a large part of the dirt, andconsequently reduce materially thebacterial content of the milk, yet theymust be of simple construction, so thatthey can be kept in a clean condition inorder to adapt them for generalpractical use. The use of such a utensilincreases materially the keepingquality of the milk.

FIG. 13.—SANITARY MILK PAILS.

The Stadtmueller pail and theTruman pail, two of the most

practical of the small-topped pails.

Stocking has shown that under ordinarybarn conditions, the use of small-topped pails reduced the number ofbacteria 95 per cent; with dirty cowsthe reduction in bacteria amounted to97 per cent. A six-inch opening

presents only one-fourth as large anexposure as a twelve inch, so that thereduction in bacterial content is greaterthan the lessening in the size of theopenings of the pails. The ordinary pailreceives dust not only from the udder,but also from the flank which is usuallya more important source ofcontamination than the udder itself,while the small-topped pail receivesonly that from the udder.

FIG. 14.—USE OF SANITARY MILK PAILS.

The open pail is fully exposed to thefalling dust while the hooded pail

excludes much of the dust and dirtcoming from the animal.

Milking machines. Where the milk isremoved from the udder by machinemethods, instead of by hand, it ispossible to eliminate nearly all external

contamination from the animal and hersurroundings. The only opportunity forinfection is then through the leakage ofair around the teat cups. Care should betaken to see that the teats are in a cleancondition before applying the suctioncups. The main problem in the use of amilking machine is to keep theapparatus in an aseptic condition.Immersion of the teat cups and therubber connections in lime water, brinesolution, or other mild antiseptics,prevents bacterial development.Hastings has found that milk having agerm content of less than 10,000bacteria per cubic centimeter may beproduced by the use of a properlyhandled milking machine.

Contamination from the milker.While the milker is a small factor incomparison with the animal in thematter of contamination, yet he can notbe neglected, as it is within his powerto affect profoundly the quality of themilk. His personal habits as tocleanliness and his appreciation of theprecautions necessary in the productionof clean milk have much to do with thecontamination of the milk. The milkingshould be done with dry hands,although a little vaseline may be usedwith effect. The hands should bewashed before milking as milk iscertain to come in contact with them tosome extent. The milking should bedone with the whole hand rather than

stripping between the thumb andfinger; the clothing should be coveredwith clean overalls and jumper, or atleast a clean apron should be wornduring the milking. If these are ofwhite material, more frequentlaundering is likely to result.

Contamination from air. It is difficultto disassociate the contaminationarising from the condition of the airfrom that derived directly from theanimal. Barn operations of variouskinds result in the production of dust,particularly where dry forage, such ashay or straw, is handled. Where manureis given an opportunity to dry, dust isreadily produced, and such material isparticularly replete with bacterial life.

Some kinds of dust, such as thatoriginating from ground grains, orshavings that may be used for bedding,contain a small amount of bacterial lifein comparison with the dust from hay,or other dry fodder. In a driedcondition, the slightest movement isapt to dislodge these fine particles, andthey float in the air for considerableperiods of time. If milk is drawn andexposed to the air of the barn duringthe feeding operations, it is subject tothe dust shower that is present. Wherethe storage can is allowed to stand inthe stable during the milking, eventhough it is covered with a strainer, thisaccumulation of microscopic particlesis added to the milk, as they readily

pass the meshes of the finest strainer.

FIG. 15.—CONTAMINATION FROM THE AIR.

This culture plate, three inches indiameter, was exposed for 30 seconds

in the barn during feeding of dryfodder. A 12-inch pail exposes over18 times the surface of this plate.

Removal of dirt after introduction.The more primitive method ofimproving the quality of milk, so far asits dirt content is concerned, is toattempt to remove the grosser particlesof contamination after entrance. In thecase of straining, the method is usuallyapplied at the time of milking, but inthe case of filtering and clarifying, it iscarried out at the milk station, in aneffort to improve the appearance ofmilk and overcome the influence ofcareless methods of the producer. Bythe use of strainers, either metallic orcloth, it is possible to remove particles

of hair, undissolved dirt and manure,but it must be remembered that thesegrosser visible particles of pollutionare not really the cause of the troubleswhich may ensue in improperlyhandled milk. The bacteria which areadherent to these foreign particles arein large measure washed off in theprocess of straining, and pass throughthe meshes of the finest strainer. Themain service, therefore, of straining isto improve the appearance of the milk,and it has no effect on the quality inany way.

Production of clean milk. Theproblem of clean milk is important,whatever may be the use to which milkmay be put. It is important in the

manufacture of butter, but owing to thefact that the fat is not readily actedupon by bacteria, it is not so sensitiveto bacterial conditions, as when themilk is made into cheese. In thisproduct, the bacterial condition of themilk is a matter of prime importance.In milk destined for directconsumption, the exclusion of thebacteria becomes yet more important.While it is impossible to excludebacteria so completely that milk willnot undergo fermentative changes, yetfor domestic consumption it ispreferable to have milk with as lowbacterial content as can readily besecured. The highest type of marketmilk, that known as sanitary, or

certified, is produced under suchextreme conditions of care as tocontain the minimum germ content. Toaccomplish these results requires suchstringent control as to increase greatlythe cost of the product. Pure, cleanmilk can be produced at a very slightincrease in cost over the regularexpense of milk production, if the rightkind of attention is given to certaindetails of a practical character.Improvement in our milk supplies mustlargely come from this source, for anyimprovement to be permanent must bemade to pay, and it requiresconsiderable education to secure theco-operation of consumers and theirwillingness to pay for any material

increase in the quality of the product.

In the foregoing factors concerned inthe contamination of milk, it is ofcourse impossible to measureaccurately the influence of the differentsources of infection, as these arecontinually subject to variation inevery case. As a rule, the mostimportant factors are those pertainingto the utensils and the condition of theanimal herself. If these two factors arebrought under reasonable control, themajor portion of contamination thatordinarily obtains is done away with.The application of the remedial orpreventive measures heretoforementioned will greatly reduce the germcontent of the milk.

Cooling of milk on farm. Bacterialgrowth is directly related totemperature conditions, and withsummer temperatures, suchdevelopment goes on apace, unless it ischecked by early cooling. The largerportion of bacteria that find their wayinto milk, especially those that arepreviously in contact with the air, arein a dormant condition, and aretherefore not stimulated intoimmediate growth, unless reasonablyhigh temperatures prevail. In milk,which comes from the animal at bloodheat, this growth is greatly stimulated.To counteract this effect, milk shouldbe chilled as soon after milking aspossible. If the temperature is

immediately lowered to 50° F., orlower, actual cell development isgreatly retarded, and the rate ofsouring, and other fermentativechanges thereby diminished. In thiscountry ice is liberally used inaccomplishing this result. In Europe,the use of ice is much less common.The employment of such artificialmeans of refrigeration makes possiblethe shipment of milk for long distancesby rail. New York city now receivesmilk that is produced in Canada andnortheastern Ohio.

FIG. 16.—EFFECT OF COOLING MILK.

Aeration of milk. The custom has beenextensively recommended ofsubjecting milk to the influence of airin the belief that such exposure permitsof the interchange of gases that wouldimprove the quality. In practice, thisprocess, known as aeration, is carriedon in different ways. In some cases, airis forced into the milk; in others, the

milk is allowed to distribute itself in athin sheet over a broad surface, fallingin drops or tiny streams through the air.Whenever this process is carried on ata temperature lower than that of themilk, it results in more or less rapidcooling.

In earlier times, aeration was generallyrecommended and practiced, especiallyin connection with the cheese industry,but carefully controlled experimentsfail to show that the process exerts anymaterial influence on the rate of germdevelopment. If it is carried out in anatmosphere more or less charged withbacteria, as in the barn or stable, it ismore than likely to add to the bacterialcontent of the milk. While to some

extent odors may be eliminated by theprocess, the custom is not followed sogenerally now as it used to be someyears ago.

Absorption of taints. A taintedcondition in milk may result from thedevelopment of bacteria, acting uponvarious constituents of the milk, andtransforming these in such a way, as toproduce by-products that impair theflavor or appearance of the liquid; or itmay be produced by the milk beingbrought in contact with any odoriferousor aromatic substance, underconditions that permit of the directabsorption of such odors.

This latter class of taints is entirely

independent of bacterial action, and islargely attributable to the physicalproperty which milk possesses ofabsorbing volatile odors. This directabsorption may occur before the milkis withdrawn from the animal, orafterwards if exposed to strong odors.

It is not uncommon for the milk ofanimals advanced in lactation to have amore or less strongly marked odor andtaste; sometimes it is apt to be bitter, atother times salty to the taste. It is adefect that is peculiar to individualanimals, and is liable to recur atapproximately the same period inlactation. The peculiar "cowy" or"animal odor" of fresh milk is aninherent peculiarity that is due to the

direct absorption of volatile elementsfrom the animal herself.

Many kinds of feed consumed by theanimal produce a more or lesspronounced taint or flavor in the milk.With some plants, such as garlic, leeks,turnips, and cabbage, the odor is sopronounced as to render the milk quiteunfit for use. In some states along theAtlantic seaboard, wild plants of thischaracter in woodland pastures may beso abundant as to make it impossible topasture milch animals. The difficultyin such cases is due to absorption of thevolatile principles into the circulationof the animal, and if such feed isconsumed shortly before milking, thecharacteristic odors appear in the milk.

If consumed immediately after themilk is withdrawn from the animal,sufficient time may elapse so that thepeculiar odors are dissipated before themilk is again secreted. The sameprinciple applies in a lesser degree tothe use of certain green fodders that aremore suitable for feed, such as rape,green rye, or even silage. Silageproduces a distinct, but not unpleasantodor in milk, but newly pastured ryeoften confers so strong an odor as torender the milk unusable.

Where certain drugs are employed inthe treatment of animals, such asbelladonna, castor oil, sulfur, orturpentine, the peculiar odors mayreappear in the milk. Such mineral

poisons as arsenic have been known topersist for a period of three weeksbefore elimination.

On account of the elimination of manydrugs, unchanged, from the animal inthe milk, the milk of any animal that isreceiving medicine should not be usedfor human food. When such milk ismixed with that of a number of otheranimals and when it is used by adults,no harm is likely to result, but whenthe dilution is not great and the milk isused for young children it may affectthem through its content of the drug.The feed may not only affect thequality of milk but its value as food.One of the most prominent ofAmerican dairymen, who has for many

years produced milk especially forchildren's use, has said that he couldfeed his cows so as to make ill everychild receiving the milk.

Absorption of odors after milking. Ifmilk is brought in contact with strongodors after being drawn from theanimal, it will absorb them readily, asin the barn, where frequently it isexposed to the odor of manure andother fermenting organic matter.

It has long been a popular belief thatmilk evolves odors and cannot absorbthem so long as it is warmer than thesurrounding air, but from experimentsof one of us (R), it has been definitelyshown that the direct absorption of

odors takes place much more rapidlywhen the milk is warm than when cold,although under either condition, itabsorbs volatile substances quiterapidly.

The custom of straining the milk in thebarn has long been deprecated asinconsistent with proper dairy practice,and in the light of the aboveexperiments, an additional reason isevident why this should not be done.

Even after milk is thoroughly cooled, itmay absorb odors, as is noted wherethe same is stored in a refrigerator withcertain fruits, meats, fish, etc.

Distinguishing bacterial from other

taints. In perfectly fresh milk it isrelatively easy to distinguish betweentaints caused by the growth of bacteriaand those attributable to directabsorption. If the taint is evident attime of milking, it is in all probabilitydue to character of feed consumed, orpossibly to medicines. If, however, theintensity of the taint grows morepronounced as the milk becomes older,then it is probably due to livingorganisms which require a certainperiod of incubation before their by-products are most evident.

Moreover, if the difficulty is ofbacterial origin, it can be frequentlyproduced in another lot of milk (heatedor sterilized is preferable) by

inoculating the same with some of theoriginal milk. Not all abnormalfermentations are able, though, tocompete with the lactic acid bacteria,and hence outbreaks of this sort soondie out by the re-establishment of morenormal conditions.

Factory contamination. As the timeelement is of importance in theproduction of troubles due to bacteria,it follows that infection of milk on thefarm is fraught with more consequencethan factory contamination, as theorganisms introduced would have alonger period of development.Nevertheless, the conditions in thefactory are by no means to be ignored,as they not infrequently permit the

milk to become seeded with highlyundesirable types. A much more rigidcontrol can be exercised in the factory,where steam is at hand as an aid in thedestruction of organisms. In thecleaning of pumps and pipes, steam isabsolutely necessary to keep suchapparatus in a sanitary condition.

The water supply of the factory is amatter of prime importance, as water isused so extensively in all factoryoperations. When taken from a shallowwell, especially if surface drainagefrom the factory is possible, the watermay be contaminated to such an extentas to introduce undesirable bacteria insuch numbers that the normal course offermentation may be changed. The

quality of the water, aside from flavor,can best be determined by making acurd test (p. 99) which is done byadding some of the water to boiledmilk, and incubating the same. If"gassy" fermentations occur, itsignifies an abnormal condition. Indeep wells, pumped as thoroughly as isgenerally the case with factory wells,the germ content should be very low,ranging from a few score to a fewhundred bacteria per cubic centimeterat most. The danger from ice is muchless, for the reason that good dailypractice does not sanction using icedirectly in contact with milk or cream.Then, too, water is largely purified inthe process of freezing, although if

secured from a polluted source,reliance should not be placed in thismethod of purification, for evenfreezing does not destroy all vegetatingbacteria.

The ordinary house fly is an importantsource of contamination in creameries,cheese factories and city milk plants.They are of importance not only inincreasing the number of fermentativebacteria in milk but they may serve tocontaminate it with disease-producingorganisms. The windows of all placeswhere milk is handled, whether on thefarm or elsewhere should be screened.

It should be kept in mind in thehandling of milk and other dairy

products that human food is beingprepared and that cleanliness isdesirable from every point of view, andthat the methods of handling andproduction should compare with thoseused in the preparation of foods whichlike milk cannot be cleaned when oncepolluted. Desirability, keeping quality,healthfulness and the value of everyproduct made from milk depends uponthe extent and amount ofcontamination.

CHAPTER IV.

INFECTION OF MILKWITH PATHOGENIC

BACTERIA.

That the disease-producing, orpathogenic bacteria, are able to infectmilk supplies is shown by the fact thatnumerous epidemics of contagiousdisease have been directly traced tomilk infection. Milk is generallyconsumed in a raw state, and as aconsiderable number of this class oforganisms are able not only to live but

actually grow in milk, which is such anideal culture-medium for thedevelopment of most bacteria, it is notsurprising that disease processesshould be traced to this source. Theorganisms in milk capable of causingdisease do not alter or change itsphysical properties sufficiently toenable their presence to be detected bya physical examination.

Origin of pathogenic bacteria inmilk. Disease-producing bacteria maybe grouped, with reference to theirrelation toward milk, into two classes,depending upon the manner in whichinfection occurs:

Class I. Disease-producing bacteria

capable of being transmitted directlyfrom a diseased animal to man throughthe medium of infected milk.

Class II. Bacteria pathogenic for manbut not for cattle, which are capable ofthriving in milk after it is drawn fromthe animal.

In the first group, the disease producedby the specific organism must becommon to both cattle and man. Theorganism must live a parasitic life inthe animal, developing in the udder,and so infect the udder. It may, ofcourse, happen that diseases towardwhich domestic animals alone aresusceptible may be spread from oneanimal to another in this way without

affecting human beings.

In the second group the bacterialspecies live a saprophytic existence,growing in milk, as in any othernutrient medium, if it happens to findits way therein. In such cases, milkindirectly serves as an agent in thedissemination of disease, by givingconditions favorable to the growth ofthe disease germ.

By far the most important of diseasesthat may be transmitted directly fromanimal to man through a milk supply istuberculosis, but in addition to this,foot and mouth disease (aphthous feverin children), Malta fever, and acuteenteric troubles have also been traced

to a similar source of infection.

The most important specific diseasesthat are disseminated throughsubsequent infection of the milk aretyphoid fever, diphtheria, scarlet fever,and cholera, but, of course, thepossibility exists that any disease germcapable of living and thriving in milkmay be spread in this way. In additionto these diseases that are caused by theintroduction of specific organisms (thecausal organism of scarlet fever has notyet been definitely determined), thereare a large number of more or less illydefined troubles of an intestinalcharacter that occur especially ininfants and young children that areundoubtedly attributable to the activity

of micro-organisms that gain access tomilk during and subsequent to themilking, and which produce changes inmilk before or after its ingestion thatresult in the formation of toxicproducts.

Tuberculosis. This disease is by far themost important bacterial malady thataffects man and beast. In man, itassumes a wide variety of phases,ranging from consumption,tuberculosis of the lungs, which is byfar the most common type, toscrofulous glands in the neck, coldabscesses, hip-joint, and bone diseases,as well as affection of the bowels.These various manifestations are allproduced by the inroads of the specific

organism, Bacillus tuberculosis. Thebovine, as well as swine, fowls, andother warm-blooded animals, are alsoaffected with similar diseases. In man,the importance of the malady isrecognized when it appears that fullyone-seventh of the human race die ofthis scourge. In cattle, the disease isequally widespread, particularly inthose countries where live stock hasbeen intensively developed. In thenorthern countries of Europe, such asDenmark, Germany, England, France,and the Netherlands, as well as inCanada, and this country, this diseasehas been most widely disseminated.This has been occasioned, in largemeasure, because of the exceedingly

insidious nature of the disease in cattle,thereby permitting interchange of suchdiseased stock without the diseasebeing recognized. Tuberculosis isfound more abundantly in this countryin dairy than in beef stock. Dairy cattleare, however, not more susceptible, butthe closer environment in which milchcattle are kept, and the fact that therehas been greater activity in the matterof introducing improved strains,accounts for the larger percentage ofaffected animals.

It has been a disputed question forsome years whether the organismsproducing bovine and humantuberculosis are identical or from thepractical standpoint, whether the

bovine type of disease is transmittedunder natural conditions to man. Thebacteriologist can readily detectdifferences in appearance, in growth ofcultures, and in disease-producingproperties between the two strains. Ofthe two, the bovine is much the morevirulent when inoculated intoexperimental animals. In aconsiderable number of cases, recordof accidental infection from cattle toman has been observed. These haveoccurred in persons makingpostmortem examination ontuberculous animals, and the tubercularnature of the wound proven by excisionand inoculation.

More recently, since the agitation by

Robert Koch of Germany, a number ofscientific commissions have studiedparticularly the problem oftransmission. It is now estimated thatperhaps seven per cent of thetuberculosis in man is of bovine origin.This is almost wholly confined tochildren. The portions of the body thatbecome diseased, when the infectionhas resulted from the use of milk, arethe glands of the neck and of theabdomen.

Manner of infection in man. In themain, the source of the malady may betraced either to air infection or to thefood, if one disregards thecomparatively small number of casesof wound infection. Air is frequently a

medium by which the germ istransferred from one person to another.The sputum is exceedingly rich intubercle bacilli and since this materialis carelessly distributed by tubercularpeople, the air of the cities, villagesand public buildings will frequentlycontain tubercle organisms. Some ofthe organisms in the air find their wayinto the lungs, there to develop andproduce consumption. The organismsin the air may be deposited in the nasalpassages and throat, and ultimatelyfind their way into the tissues of thebody by penetrating the walls of thethroat or of the intestine. It is probablethat the tubercle bacilli thus introducedmay find their way to the lungs and

there develop without leaving any traceof their path.

Food may also possibly serve as amedium of infection. Thecontamination of solid food from fliesand other sources is, of course, apossibility, but tuberculous meat fromcattle and swine is much more likely tooccur, although it must be said that theprocesses of preparing such food foruse (roasting, frying, and boiling) aresufficient to destroy the vitality of thecausal organism. The fact that mostfood products of this character are nowinspected renders this possibility lesslikely to occur.

Unquestionably, the likelihood of

ingesting tubercle organisms is muchgreater with milk than with any otherfood supply, as milk is consumedusually in an uncooked state, and asmicroscopic and physiologic testsindicate that not infrequently milkfrom tuberculous animals containsthese organisms.

Distribution of the disease inanimals. As practically any organ ofthe body may be affected withtuberculosis, it naturally follows thatthe lesions of this disease are widelydistributed. The disease germ isintroduced, in the main, through thelymph and not the blood system;consequently, in the initial stages theevidence of tuberculosis is often

comparatively slight, and the lesion isrestricted in its development. Wheresuch a condition obtains, it is known as"closed," in contradistinction to "open"tuberculosis, where the diseased tissueis more or less broken down and isdischarging into the circulation, orelsewhere. Manifestly, the danger ofspreading not only in the affectedanimal itself, but to the outside, ismuch greater in the case of the openlesion. Especially is this true where thedisease is present in the lungs or organsthat have an exterior opening so thatthe material containing the organismsis discharged from the body in thesputum, manure, urine or milk. Theintestines themselves are rarely

affected, but the lymph glandsassociated with the intestinal tract arenot infrequently involved.

Infection of milk with tuberclebacilli. In a small percentage of cases,the udder itself becomes involved.Where this condition obtains, one ormore hard lumps are formed, whichslowly increase in size, usually beingrestricted to one quarter of the udder.Sometimes the affected quarter maydevelop to an enormous size, producinga hard, painless tumor. Not often doesthe affected tissue break down into pus;consequently, no abnormal appearanceis to be noted in the milk secretionuntil the disease has made veryextended progress, in which case the

percentage of fat generally diminishes.Whenever the udder shows physicalmanifestation of this disease, the milkalmost invariably is rich in tuberclebacilli.

Tubercle organisms may also appear inmilk of animals in which no physicalsymptoms of the disease are to befound. This fact has been demonstratedby microscopic and animalexperiments, but it is also abundantlyconfirmed by the frequent contractionof the disease by calves and hogs whenfed on factory by-products. This latterclass of animals is particularlydangerous, because there is no way inwhich the danger can be recognized.

FIG. 17.—A TUBERCULOUS ANIMAL.

The animal appears perfectly healthyalthough she has had the disease for

five years.

It has also been proven that milk maybecome infected through the feces. Incoughing up material from the lungsand associated glands, the matter is

swallowed, instead of expectorated, asin man. The organisms retain theirvitality in the intestine, and are voidedin the feces. Under ordinary conditions,the flanks and udder become more orless polluted with such filth, and theevidence is conclusive that infection ofmilk is not infrequently occasioned inthis way. The fact that hogs followingtuberculous steers in the feeding lotsare very likely to acquire the disease isexplained by the presence of tubercleorganisms in the manure of suchanimals.

FIG. 18.—A TUBERCULOUS ANIMAL.

The last stages of generalizedtuberculosis. Note the emaciated

condition.

It must be kept in mind that manyanimals may be infected with tuberclebacilli and therefore have tuberculosisin the incipient stages, without their

being able to disseminate the disease toothers. In the early stages, they arebacillus-carriers without beingnecessarily dangerous at that particulartime, but the possibility always exists,as the disease develops in the system,that the trouble may assume a moreformidable character, and that slowlydeveloping chronic lesions maybecome acute, and "open," in whichcase, the affected animal becomes apositive menace to the herd. As thetime when the lesions change from the"closed" to the "open" type and theanimal becomes a source of dangercannot be determined, the only safeway to do is to exclude the milk of alltuberculous animals from the general

supply, whether for directconsumption, or for manufacture intodairy products and to look upon everydiseased animal as a menace to theherd. This is rendered all the morenecessary when the milk is used for thefeeding of children, who are relativelymore susceptible to intestinal infectionthan the adult. The early stages of thedisease in cattle are, however, soinsidious that no reliance can be placedupon the detection of the malady byphysical means. Fortunately, in thetuberculin test, a method is at hand,which in a simple, but effectivemanner, enables the disease to bedistinguished in even the early stages,long before recognition is possible in

any other way.

Tubercle bacilli in dairy products.When infected milk is used for thepreparation of butter and cheese, theorganisms inevitably are incorporatedin them. In the separation of milk arelatively large part of the tubercleorganisms in the milk appear in thecream. In the making of cheese evenmore of the organisms are held in thecurd. In butter and cheese, as in milk,no growth of the organism can takeplace; however, the vitality of theorganism is retained for a considerablenumber of months. It is not believedthat these products are of muchimportance in the spread oftuberculosis in the human family, since

they are not consumed by children toany extent. Cream is to be consideredas a means of distribution since it isoften used by children.

Treatment of tuberculous milk. It iseasily possible to treat milk or factoryby-products so as to render thempositively safe. The process ofpasteurization or sterilization isapplicable to whole milk, and wheneffectively done destroys entirely thevitality of any tubercle bacilli. Inmaking such exposure, care should betaken to prevent the formation of the"scalded layer," as the resistance of theorganism toward heat is greatlyincreased under these conditions. In aclosed receptacle, 140° F. for 15 to 20

minutes has been found thoroughlyeffective in destroying this organism.A momentary exposure at 176° F. islikewise sufficient. This is the methodthat is almost universally used inDenmark in the manufacture of thefinest butter.

In the treatment of factory by-products,heat should also be employed. InDenmark, compulsory pasteurization atnot less than 176° F. is required. Thistreatment prevents not only thedissemination of tuberculosis amonghogs and young cattle, but is equallyefficacious in preventing the spread offoot and mouth disease.

The per cent of tuberculous milch cows

varies widely in different sections ofthe country, being greatest in the olderdairy sections, and in those supplyingmilk to the cities, on account of theconstant buying and selling of animals,thus giving more frequent opportunityof introducing the disease into theherds. Throughout the country at large,probably less than ten per cent of thecows are tuberculous, and it isestimated that at least one per cent ofthe diseased animals have tuberculousudders. It has been suggested that thedilution of the milk of such animalswith that of healthy cows wouldremove a great part of the danger frommilk. In the case where the milk of alarge number of herds is mixed, this

may be of some importance, but in nocase is it safe to assume that dilution ofthe milk of tuberculous cows is anyguarantee of safety.

It has been shown that milk, perfectlynormal in appearance, coming from atuberculous udder could be diluted amillion times and still produce thedisease on inoculation intoexperimental animals. In the case ofswine, the susceptibility is so great thata single feeding of infected milk, evenin a very dilute condition, causes withcertainty the production of the disease.

Some observers maintain that thecontamination of the milk with themanure of tuberculous animals is of

greater hygienic importance, than thatcoming from diseased udders, since thenumber of animals having tuberculosisof the lungs and intestines is far greaterthan those with diseased udders.

Economic aspects of bovinetuberculosis. Not only is this diseaseinvested with much importancebecause of its inter-relation with thehuman, but from an economic point ofview alone, it is undoubtedly thegreatest scourge that affects thedairyman. Its insidiousness makes itexceedingly difficult to recognize. Theconsequence is that many fine herdsbecome seriously involved before itspresence is recognized. In the main, thedisease is introduced into a herd by

purchase, often by buying in pure-bredstock to improve the quality of theherd. Where the disease has beenestablished in a region for some time,there is also danger that unheatedfactory by-products, as skim milk andwhey, may function in its spread.Where such conditions prevail, thespread of the disease in the creamerydistrict is exceedingly rapid. Whenonce introduced into a herd, the diseasesooner or later spreads from theoriginally affected animal to others inthe herd. Close contact, and closeconfinement in ill ventilated stablesfacilitate the spread of the disease, andsooner or later, other animals acquirethe trouble. This may all occur while

all animals appear in a healthycondition.

The symptoms of the disease in theearlier stages are quite indefinite. Asthe disease progresses, the nutritivefunctions appear to be disturbed, andsooner or later, the body weight beginsto decline, and finally markedemaciation ensues. Accompanying thiscondition, especially when the diseaseis in the lungs, is a cough, which isgenerally aggravated with activeexercise. While the run-down conditionpermits frequently of the detection ofthe disease in the advanced stages, it iswholly impossible with any accuracy todiagnose the trouble in the incipientstages. It is at this stage that the

tuberculin test comes to the aid of thestockman.

Tuberculin test. This test is made bythe injecting beneath the skin of theanimal a small quantity (about 2 c. c.)of tuberculin, and noting thetemperature of the animal, before andafter the injection. Tuberculin, aproduct of the growth of the tuberclebacillus, when injected into the bodycauses a marked rise in temperature, inthe case of an animal affected with thedisease, and no such elevation in thecase of a healthy animal. The processof preparing tuberculin makes itabsolutely free from danger, so far asliability of producing the disease, or inany way injuring the animal, is

concerned. Fig. 19 shows thetemperature range of both reacting andnon-reacting animals. While the test isnot absolutely infallible, it is so farsuperior to any and all other methodsof diagnosis that it should takeprecedence over them.

Miscellaneous diseases. There are anumber of diseases that affect bothhuman beings and cattle, the causalorganisms of which may be transmittedthrough the milk. Foot and mouthdisease is one wide spread in Europeancountries but which has not yet gaineda permanent foothold in this country.The ingestion of the milk, whichalways contains the causal organism,produces the disease in both humans

and cattle. In the human the disease isvery similar to that in cattle; it mayend in death. Vesicles are produced inthe mouth, on the lips, nose andfingers. The causal organism, whichhas not yet been demonstrated, mayoccur in butter or cheese. It is easilydestroyed by pasteurizing the milk.

FIG. 19.—TEMPERATURE CURVES.1, the temperature curve of a healthy

animal after injection withtuberculin; 2 and 3, the temperaturecurves of tuberculous animals after

injection with tuberculin. (AfterMoore.)

Anthrax, actinomycosis (lumpy jaw),rabies, and malta fever are diseases theorganisms of which have been found inthe milk of affected animals. In case ofthe first three, while the possibilityexists of the infection of human beingsby milk, it is improbable that suchinfection does normally occur. Maltafever is becoming an important diseasein portions of southern Europe. It isproduced in man by the use of milk ofgoats suffering from the disease.

The organism causing contagiousabortion in cattle is known to bepresent in the milk of the infectedanimal at the time of its withdrawalfrom the udder. It is not probable thatthe organism is of any sanitarysignificance as far as man is concerned.It has been shown that the organism isable to produce a disease in guinea pigson artificial inoculation that is verysimilar, so far as the lesions areconcerned, to tuberculosis. It is alsoprobable that the by-products ofcreameries and cheese factories mayserve to spread the disease from oneherd to another.

Inflammation of the udder (garget) is afrequent trouble in every herd. It is

marked by the swelling of one or morequarters, by the appearance of feverand changes in the appearance andcomposition of the milk. Theinflammation may be caused by cold orinjury, or by the invasion of the udderwith pus-forming bacteria. In the firstcase the trouble is not likely to persistfor any length of time, and does notspread to other members of the herd.The milk may be more or less stringy,and may show a slimy flocculentsediment. It cannot be asserted thatsuch milk is harmful to man but itshould be rejected on general sanitarygrounds, and because it cannot alwaysbe differentiated from that comingfrom an udder in which the

inflammation is produced by bacteria.

Inflammation caused by the invasion ofthe udder with specific bacteria isusually of greater severity, the entiregland often becoming involved. Thesecretion of milk may cease and thefunction of the diseased quarters maynever be restored. The milk in the lesssevere cases may not be abnormal inappearance, but with increasingseverity, the nature of the milkchanges, until it may be a wateryliquid. The milk of any animalsuffering from any form of gargetshould be rejected, as it may causetrouble, especially in children. There issome reason to believe that organismscoming from cases of garget have been

responsible for the extensive outbreaksof septic sore throat that have occurredin some parts of the country.

The milk of animals suffering fromindigestion, diarrhea, abscesses on anypart of the body, as from those whichhave retained the afterbirth should belikewise rejected. In short only themilk of healthy animals should be usedfor human food; that from any animalsuffering from any disease or which isreceiving medical treatment should notbe so used.

Typhoid fever. The most importantdisease germ, distributed through themedium of milk, that is unable toproduce a diseased condition in the

cow is the organism of typhoid fever.This malady is an intestinal afflictionof man, and the germ causing the sameis found abundantly in the dejecta, bothsolid and liquid, as well as in the bloodin certain stages of the disease. Whilethe causal organism does not leave thebody through the expired air, it isfound abundantly in both the urine andfeces. Therefore, the dejecta, and anyarticles that may be soiled with thesame become a positive menace.

Many different methods oftransmitting the contagion exist, suchas water, food infected in various ways,contact with infected persons, andthrough the medium of milk. Milk isnot so frequently the cause of

dissemination as the other factors, butwhere milk supplies becomecontaminated, epidemics ofconsiderable magnitude are wont tooccur. The danger from milk is alsoaggravated by the fact that the typhoidbacillus is capable of withstandingconsiderable amounts of acid, andconsequently finds, even in raw milkcontaining the normal lactic acidbacteria, conditions favorable for itsgrowth. In a considerable percentage ofcases, the disease is not sufficientlysevere to cause the patient to take tohis bed. These so-called "walkingtyphoid" cases are particularlydangerous, because they serve tospread the disease organism more

widely.

A very considerable proportion of thepeople that recover from typhoid feverstill continue to harbor the typhoidbacillus in their urinary and gallbladders. This condition may obtain foryears, and since such individuals are inperfect health and are ignorant of theirown condition, and since they give offthe organisms more or less constantly,they are often the cause of extensivemilk borne epidemics. Such personsare known as "typhoid carriers" andconstitute one of the gravest problemsthe public official has to contend within his struggle to prevent the spread oftyphoid fever.

Where outbreaks are caused by milk,they can readily be traced by means ofthe milk route, as there are always asufficient number of susceptiblepersons, so that outbreaks of epidemicproportions develop. In the Stamford,Conn., outbreak in 1895, 386 casesdeveloped on one milk route. In thiscase it was shown that the carryingcans were thoroughly washed, but werelater rinsed out with cold water from apolluted shallow well.

The mode of infection of milk varies,but in general, the original pollution isoccasioned by the use of infected waterin washing the utensils, or a case of"walking typhoid" or bacillus carrier,who directly infects the milk. In case

of sickness in rural families, somemember of the household may serve inthe dual capacity of nurse andmilkmaid, thus establishing thenecessary connection. Busey and Koberreport twenty-one outbreaks, in whichdairy employees also acted in thecapacity of nurses. The fact that theurine of a convalescent may retain thetyphoid germ in large numbers forsome weeks renders the danger fromthis source in reality greater than fromfeces, as, naturally, much less care isexercised in the disposition of theurine.

The house fly is now regarded as one ofthe important means of spreadingtyphoid fever, indeed it is often called

the "typhoid fly." The infectiousmaterial deposited in an open vaultmay serve as a source from which thefly carries the organisms to milk andother foods in the house or elsewhere.The protection of vaults and thescreening of every place where humanfood is handled or prepared is the onlyprotection.

It should be emphasized that in thecase of the tubercle organism, nogrowth ever occurs in milk, but withthe typhoid bacillus growth is possible.It thus needs but the contamination ofthe milk with the smallest particle ofmaterial containing them to seed themilk. By the time it is consumed it maycontain myriads of the disease-

producing organisms.

Diphtheria. This is a highly infectiousdisease, affecting children primarilyand is characterized by the formationof membranous exudates in the throatand air passages, which are teemingwith the causal organism, thediphtheria bacillus. This organism iscapable of forming highly toxicproducts, and it is to the effect of thesepoisons that its fatal result is generallydue. The organism is thrown out fromthe body, in the main, through themouth, the surroundings of the patientbeing infected directly from the air,and indirectly, by contact with pollutedhands, lips, etc. Thus, the germdeposited from the lips of a case of the

disease, on the common drinking cup,slate, lead pencils, toys, and the like,may easily pass from child to child.Not infrequently, the causal organismpersists in the throat long after allevidence of membranous growth hassubsided, and so the child itself mayact as a "bacillus carrier."

Not so many epidemics of diphtheria asof typhoid have been traced to milk,but the evidence is sufficient to indictmilk as a disseminator of contagion. Inseveral cases, the diphtheria germ hasactually been isolated from infectedmilk supplies. Actual growth of thediphtheria germ is said to take place inraw milk more rapidly than insterilized.

Scarlet fever. While the germ ofscarlet fever has not yet been isolated,and therefore its life history in relationto milk cannot be depicted soaccurately, yet milk-borne epidemicsof this disease are sufficientlyabundant to leave no doubt but that thisfood medium may sometimes serve asa means of disseminating suchtroubles. Infection of the milkdoubtless comes in the case of thisdisease from direct contact with aperson suffering from the malady.

Cholera. While this disease is of nopractical importance in America,owing to its relative infrequency, yetoutbreaks of cholera have been tracedto milk, in spite of the fact that the

causal organism is more sensitive tothe action of acids than most disease-producing bacteria. In severaloutbreaks in India, milk has been themedium through which the disease wasspread. Generally, infection of the milkhas been traced to the use of pollutedwater.

Children's diseases. An exceedinglyhigh mortality exists among infantsand young children in the morecongested centers, especially duringthe summer months. In the main, thecause of these troubles is due tointestinal disturbances, andunquestionably, the character of thefood enters largely into the problem.As milk constitutes such a large

proportion of the diet of the young, andis so susceptible to bacterial invasion,it would appear probable that much ofthe trouble of this character is due tothe condition of this food supply. Thisis rendered more probable when it isremembered that bottle-fed infantssuffer a much higher mortality thanbreast-fed children, due probably to thefact that the lengthened period betweenthe time the milk is drawn andconsumed permits of abundantbacterial growth. Much carelessnessalso prevails among the poor in cities,relative to the care of utensils used infeeding children. Nursing bottles oftenserve to infect the milk. Where milk ispasteurized, or properly heated, it has

been found that the mortality rate hasbeen greatly reduced, thus indicatingthat the condition of the milk wasdirectly responsible for the death rate.In fact, the mortality from theseindefinite intestinal troubles probablyexceeds that from all of the specificinfectious diseases combined.Improved care in handling thissensitive food supply will do much tobetter conditions in this direction.

Ptomaine poisoning. Acute poisoningaffecting adults as well as children, notinfrequently occurs from the use offoods of various kinds. Cases ofpoisoning arising from the use of shellfish, canned meats, ice cream, cheese,and other dairy products, are from time

to time reported. These troubles aredue to the production of toxiccompounds, in the main, probablycaused by bacterial decompositions.Often such troubles may affect anumber of persons, as at banquets andsuch gatherings, thereby giving thesemblance of an epidemic. While suchtroubles are doubtless to be ascribed tobacterial activity, they are nottransmissible from person to person.

In the case of troubles arising from icecream and such confections, theprobable cause is due to the storage ofmilk or cream under refrigeratorconditions, where germ growth can goon in the product, and yet thetemperature be sufficiently low to

prevent the usual acid fermentations.

CHAPTER V.

FERMENTATIONS OFMILK.

Milk, under normal conditions, isalways contaminated with bacteriacoming from the most varied sources.If it is produced under cleanconditions, the number of bacteria willbe small, but in any case, the numberof kinds of bacteria that find their wayinto milk will be large. Many of themfind in milk at ordinary temperaturessuitable conditions for growth; they use

a portion of some of the constituents ofthe milk as food, producing certainother compounds that are known as"by-products." These by-productsimpart to milk a taste and odor that isnot found in fresh milk. The effect ofthe action of bacteria may also be madeevident by the change in theappearance of the milk. When thesevarious changes become evident to thesenses, either by taste, smell or sight,the milk usually is so modified as to beunfit for many ordinary purposes. Thepreservation of milk, a subject to betreated later, is a study of the ways ofpreventing or retarding the growth ofbacteria in milk, and thus delaying thetime when evidences of their action

first become apparent.

Each class of bacteria produces moreor less specific changes in the milk as aresult of their growth. Certain bacteriaare of the greatest benefit to the butterand cheese maker, while others aredistinctly harmful to the manufacturerof dairy products. The changesproduced by the different bacteria arecalled "fermentations" of milk, eachbeing most commonly named from themost important by-product formed.

Acid fermentation of milk. Fresh milkhas a sweet taste and little or no odor,but if it is allowed to stand at ordinarytemperatures, it sours; the taste is nolonger sweet because the sweetness of

the sugar of the milk is masked by theacid produced from the decompositionof a portion of the sugar by thebacteria. The change in odor and tasteof milk is apparent long before theappearance is altered and increases inintensity as the acid-fermentationprogresses. The first alteration inappearance is most usually one ofconsistency; the liquid milk istransformed into a semi-solid mass.The terms "curdling" and "sour" areusually synonymous. Milk is, however,often said to be sour as soon as the acidfermentation has progressed to a pointwhere it is evident to taste or smell.This process of souring, or the acidfermentation is so common a change

that raw milk which does not show thistype of fermentation is looked uponwith suspicion, and, usually, justly so.The process in the past was thought tobe something inherent in the milk, anatural and inevitable change. It is nowknown that this is not so, but that it isdue to certain kinds of bacteria, andthat if these are prevented from gettinginto milk, it will not sour, but willundergo some other less desirable typeof decomposition.

The acid-forming bacteria comprisebut a very small part of the totalnumber of organisms that find theirway into the milk during its productionon the farm, yet in sour milk scarcelyany other kinds of bacteria can be

found. At ordinary air temperatures,the acid-forming bacteria grow morerapidly in milk than do any otherforms, and the acid produced by themrenders the milk an unfavorablemedium for the growth of otherbacteria. This is the reason why milkpractically always undergoes the acidfermentation, although it iscontaminated with a host of other kindsof bacteria. If a mixture of seeds issown on low wet ground, certain kindswill grow best; if the same mixture issown on drier land, other types willfind most favorable conditions forgrowth, and the plants which appearedon the low land will not appear. Thesame condition is found in milk where

the environment is most favorable forthe acid-forming bacteria.

Amount of acid formed in milk. Inthis country the acidity of milk isexpressed as so many per cent of lacticacid. A milk that shows an acidity ofone per cent should, theoretically,contain one pound of lactic acid in eachone hundred pounds of milk. The aciddetermined does not actually representlactic acid, as there are othersubstances in milk which act as acids,with the reagents used in the presentmethods of determining the acidity ofmilk. For instance, perfectly fresh milkhas an apparent acidity of 0.13 to 0.18per cent, although no fermentation hasoccurred. Other acids than lactic are

formed in the acid fermentation, butthe entire acid content is referred to aslactic when speaking of the acidity ofmilk. When the developing acidity ofmilk reaches 0.25 to 0.3 per cent, asour taste becomes evident and themilk will curdle on heating. When theacidity increases to 0.6 to 0.7 per cent,the milk curdles at ordinarytemperatures. The acidity continues,however, to increase until it reachesabout 1 per cent, which is themaximum amount that will beproduced in milk by the ordinary acid-forming bacteria. Milk contains about4 per cent of milk sugar, all of which isfermentable. If this were alldecomposed by bacteria, the acidity of

the milk would actually exceed 4 percent. It is thus evident that the reasonwhy more acid is not formed in milk isnot because of any lack of sugar. Thebacteria, like all other kinds of livingthings, are injured by their own by-products, unless these are constantlyremoved in some way; in milk thebacteria cannot escape the action of theacid which they themselves haveformed, consequently growth ceases.The amount of acid formed isdependent on the kind of bacteriapresent and on the composition of themilk. Certain bacteria will not produceenough acid to cause the curdling ofthe milk; still others will form 2 oreven 3 per cent. These types, however,

do not play any important part in thespontaneous souring of milk.

In milk the acid first formed combineswith the ash constituents and the caseinto form salts which do not seriouslyaffect the growth of the bacteria.Ultimately, the limit of the ash andcasein to take up acid is reached, andfree lactic acid which is harmful tobacterial growth appears. If the contentof casein and ash constituents is high, ahigher degree of acidity will be reachedthan in a milk with a lower content. If alarge part of the volume of the milk ismade up of a compound that has norole whatever in the acid fermentation,such as the butter fat in cream, theamount of acid formed per unit volume

of milk will be reduced, since indetermining the acidity, a definitevolume of milk is taken, and theacidity is expressed, as such a per centof this amount.

Types of acid-forming bacteria.When substances undergodecomposition, it is a common beliefthat compounds offensive to the odorand taste are formed; but such is notnecessarily the case. The products ofthe decomposition may be as agreeableand as harmless as the compoundsdecomposed. Whether thedecomposition products of anysubstance are offensive or not isdependent on the kinds of micro-organisms acting on it. There are forms

of acid-producing bacteria that changemilk in odor, taste, and appearance, yetthe sour milk is not offensive in anysense of the word. Other bacteria alsosour the milk, but produce offensiveodors and a disagreeable taste. Thus,the acid-forming bacteria may bedivided into two main groups, whichmay be designated as desirable andundesirable. This division is ofimportance to the butter and cheesemaker and to the consumer of milk.

Desirable acid-forming bacteria. Ifmilk is produced under cleanconditions, it is not likely to have adisagreeable odor or taste at any time,even when it is sour; rather the taste isagreeable like that of good butter milk.

The curd is perfectly homogeneous,showing no holes or rents, due to thedevelopment of gas, and there is butlittle tendency for the whey to beexpressed from the curd. This type offermentation is largely produced by thegroup of bacteria to which has beengiven the name, Bacillus lactis acidi.

The main by-product of this group ofbacteria is lactic acid; small amountsof acetic acid and alcohol, with tracesof other compounds, are also formed.The agreeable odor and to some extentthe flavor of milk fermented by thesebacteria is due to other by-productsthan lactic acid, for this has no odorand only a sour taste. The acidfermentation of milk is often called the

lactic acid fermentation. In reality onlythe fermentation produced by thedesirable group in which lactic acid isthe most evident by-product should bethus called.

FIG. 20.—DIFFERENT TYPES OF CURDS.On the left a solid, homogeneous

curd produced by desirable bacteria;on the right, the curd produced by

harmful bacteria. Note the gas holesand free whey.

The bacteria of this group may enterthe milk from the dust coming from thecoat of the cow. They are also found inthe barn dust and on cultivated plants.Under ordinary farm conditions, thelarger part of those found in milk comedirectly from the utensils. If the milk isdrawn under extremely cleanconditions and care is taken to sterilizethe utensils, but few acid-formingbacteria of any kind will enter themilk; under such conditions most of

the acid-forming bacteria will belongto the group in question. They find,however, such favorable conditions forgrowth in milk that they develop morerapidly than most other types withwhich milk becomes seeded;consequently under normal conditions,they gain the ascendency and so controlthe type of fermentation.

The desirable type of acid-formingbacteria do not form spores; hence, areeasily killed by heating the milk. Theycan grow in the presence or in theabsence of free oxygen. In the bottomof a can of milk or in the middle of acheese, there is no air, yet thesebacteria grow as well under theseconditions, as in milk exposed to the

air. The range of temperature forgrowth varies from 50° to 100° F. butdevelopment is most rapid at 90° to 95°F. and about 1 per cent of acid isformed.

Another group of bacteria which maybe classed among the desirable acid-forming organisms is constantly foundin milk. They have little to do with theordinary acid fermentation as theygrow very slowly at ordinarytemperatures. If a sample of raw milkis placed at the temperature of theanimal body, the acidity will reach 1per cent in a few hours. Thereafter theacidity will increase slowly and mayreach three per cent or above. Thecontinued increase in acid is due to the

growth of long rods of the BacillusBulgaricus type, which apparentlyenter the milk with the fecal matter.The nature of the change produced bythem in milk is very similar to thatcaused by Bact. lactis acidi in thatlactic acid is the chief product; no gasis produced and hence the curd isuniform in appearance. Temperaturesfrom 100° to 110° F. favor theirdevelopment. Organisms belonging tothis group are used in the preparationof the fermented milks now so widelysold in the cities.

These desirable, acid-forming bacteriaare of the greatest service in everybranch of the dairy industry, whether inbutter or in cheese making, or in the

sale of milk in the city. The dairyindustry is dependent uponfermentative activity, as much as themanufacture of beer or wine, and themain basis of this is the acidfermentation of the milk by thesedesirable types of bacteria.

Although milk contains a large amountof nitrogenous substances (casein andalbumen), it does not undergo putriddecomposition, as do meat and eggs,not because it is not fitted for thegrowth of the bacteria causing that typeof change, but because the acid formedin it stops the growth of theputrefactive bacteria. If a sample ofmilk is placed in a stoppered bottle, itwill have much the same taste and odor

at the end of several months as at theend of a few days. The acid acts as apreservative, like the vinegar inpickles, or the acid in silage and insauerkraut. Meat placed in a stopperedbottle which is then filled with milkwill be preserved.

The products formed in thedecomposition of meat and eggs arenot only offensive but may also beinjurious to the health of the consumer.Milk that has been fermented by thedesirable kinds of acid-formingbacteria is not harmful. It is consumedin a variety of forms (buttermilk,cottage cheese) as a common article offood and its use is rapidly increasing.The preparation of the pure culture

buttermilks or artificially soured milksthat are now so frequentlyrecommended for digestive troublesrests upon an acid fermentation of thistype.

Undesirable acid-forming bacteria.Other types of bacteria capable offorming substances that impart to milkan offensive odor and a disagreeabletaste not infrequently appear instead ofthe desirable group. Instead ofproducing from the sugar of milk largequantities of lactic acid, these typesgenerate other acids, such as acetic andformic, which impart a sharp taste tothe milk. Besides the acids the bacteriaof this group form gases from the sugarof the milk. Some produce small

amounts of gas; others so much that thecurd will be spongy and will float onthe surface of the whey. Thefermentation caused by them is oftencalled a "gassy fermentation" and isdreaded by butter and cheese makerssince the gas is indicative of badflavors that will appear in the product.Gas may also be produced in othertypes of fermentations to be discussedlater.

This class of bacteria enters the milkwith the dust, dirt, and manure, inwhich materials they are especiallyabundant. No spores are formed; hencethey are easily killed by heating themilk. They grow both in the presenceand in the absence of free oxygen. High

temperatures favor their growth, mostrapid development taking place at 100°to 103° F.

Spontaneous fermentation of milk.The normal souring of milk is due to amixture of these two groups ofbacteria. The relative proportionsexisting between the two in any sampleof milk is dependent on a number offactors, most important of which is thedegree of cleanliness exercised in theproduction of the milk. Where carelessconditions obtain under which dust andmanure particles find their way intomilk, it becomes more abundantlyseeded with gas-generating bacteria,and consequently, the type offermentation is undesirable. If,

however, the milk is drawn into cleanutensils and care is taken to excludedirt, the pure lactic acid types are ableto control the character of the changesproduced, and a clean, pleasant tastingliquid results. It will be seen that thingsare well arranged by nature; one of themost important food productsundergoes a type of decomposition thatis not offensive and when producedunder clean conditions, the sour milk isas healthful a food as is the freshproduct. Thus there is every reason forcleanliness in the production of milk,for cleanliness' sake and because cleanmilk means better products, and greaterreturns to everyone, producer anddealer.

There are other kinds of acid-formingbacteria in milk but they are of smallimportance compared with those justdiscussed. Some of the bacteria derivedfrom the inside of the udder of the cowform acid, but these forms grow veryslowly in milk at ordinarytemperatures, and have no influence onthe keeping quality.

FIG. 21.—DIFFERENT TYPES OF CURDS.

The flask on the left shows the softcurd produced by the bacteria that

curdle the milk without theproduction of acid. The flask on the

right shows the gassy curd formed bybutyric acid bacteria in heated milk.

Sweet curdling fermentation of milk.Samples of milk are sometimes foundthat are curdled, but which do not tastesour, or have the normal odor of sourmilk. The curd is usually soft and thetaste bitter. It is evident that thecurdling cannot be due to the samefactors as in the normal souring ofmilk. Such a change is similar to theaction of rennet which is used to curdlethe milk in cheese making. Thisferment will curdle perfectly sweetmilk, producing a curd that looks likethat formed in the acid fermentation ofmilk. The cause of these sweet curdlingmilks, which appear from time to time,

is due to the introduction of certainbacteria which have the power ofsecreting an enzyme resembling thatfound in rennet. In such cases the milkscurdle prematurely especially whenwarmed. The curd may graduallydisappear, for the bacteria also produceanother enzyme that digests the curd,and thus renders it soluble. When thisadvanced phase becomes evident, it isoften called the digestive fermentationof milk. This change is producedlargely by putrefactive bacteria ofvarious kinds that find their way intomilk with dust and dirt. Many of themare spore formers; hence, are not killedwhen milk is heated, as inpasteurization, while the acid-formers

are destroyed. Pasteurized milk is thuslikely to undergo the sweet-curdlingfermentation, if it is kept for any lengthof time. Raw milk rarely undergoesthis type of decomposition, since therennet-forming bacteria under ordinaryconditions are unable to develop incompetition with the acid-formingbacteria.

Butyric acid fermentation of milk. Afermentation that is much lessfrequently noted than the twopreviously discussed is known as thebutyric fermentation, since butyric acidis the principal by-product. The causalbacteria cannot compete with theordinary acid-forming bacteria in rawmilk; hence it is most frequently noted

in pasteurized milk, since theorganisms produce spores and are notkilled by the heating. Pasteurized milkunder the action of the butyric acidbacteria undergoes a gassyfermentation, developing a pronouncedacidity and the disagreeable odor ofbutyric acid, which resembles that ofrancid butter. The butyric acid bacteriaare anaerobic, and thus can grow inbutter and cheese away from the air.

Slimy or ropy fermentation of milk.A slimy or ropy condition of milk isfrequently noted on the farm and in thedairy. Several causes for this abnormalcondition exist. Sometimes the milkmay be slimy when milked from thecow. This occurs most frequently in the

case of inflammation of the udderwhich may or may not be due tobacteria. The direct cause of theabnormal condition in milk is thepresence of fibrin and white corpusclesfrom the blood which form masses ofslimy material; in such cases thetrouble does not increase in intensitywith age, nor can it be propogated bytransference to another sample of freshmilk.

FIG. 22.—SLIMY MILK.It does not mix with water when

poured into it.

Another type of slimy milk is producedby the growth of certain types ofbacteria which enter the milk after it isdrawn from the udder. These may comefrom various sources. The bacteriaconcerned belong to two groups: (1)those that grow best in the air and donot form acid; (2) those that grow inthe absence of air, throughout theentire mass of milk and which formacid. The slimy condition is noted inthe milk only after the milk has beenstored for some time; it usuallyincreases with the age of the milk andcan be produced in a second sample by

transferring a little of the slimy milk toit.

The fermentation produced by theaerobic bacteria is most often met inbottled milk and cream during thewarmer times of the year. On accountof their relation to oxygen, the growthis confined to the surface of the milkand only the upper layer becomesslimy; thus when the cream isremoved, the abnormal condition isnoted. The sliminess is due to the massof bacterial growth rather than to theproduction of any specific substance inthe milk. This trouble may be ofconsiderable economic importance tothe dealer, as such abnormal milk isobjectionable for ordinary use, but as

far as is known, it is incapable ofaffecting the health of the consumer.

In numerous outbreaks of this troublethe source of contamination has beentraced to infection from well water or astream, as the organisms causing thetrouble are found naturally in water.Keeping the milk in a tank in the pumphouse sometimes permits of troubles ofthis sort, the water used for coolinggiving opportunity for contamination.Cattle wading in a stream sometimespollute their udders and so indirectlyinfect the milk. Such outbreaks rarelypersist for any considerable length oftime as the common acid organismssoon regain the ascendency.

Creameries and cheese factories aresometimes troubled with sliminess instarters. This seems to be due to somechange which the ordinary lactic acidbacteria undergo on long propagationrather than to contamination of thestarter. There are, however, types ofacid-producing bacteria that are able toform specific substances in milk thatare slimy in character. Two of theseforms of slimy milk are of economicimportance. The slimy whey (langeWei) of Holland is added to milk in themanufacture of Edam cheese,apparently serving the same purpose asthe addition of the pure culture starterin cheddar cheese making. In Norway,a sour, slimy milk (taettemjolk) is used

as food. It is produced by the additionof some previously fermented milk.This beverage is also used in some ofthe Norwegian settlements ofWisconsin, the original seed havingbeen brought from Norway, and thebacteria maintained by constantpropagation from one sample of milkto another. The milk has the odor andtaste of butter milk, but is notespecially appetizing in appearance toany one not accustomed to it; it is,however, as harmless to health as isany other form of sour milk. It is notknown that any of these forms of slimymilk are distinctly harmful to thequality of butter or cheese.

Alcoholic fermentation of milk. The

bacteria as a class are incapable ofproducing alcohol in appreciableamounts. The alcoholic beverages,beer, wine, and cider, are produced bythe growth of yeast, in such sugarcontaining liquids as fruit juices,extracts of grains, etc. The commontypes of yeasts are incapable of actingon milk sugar, but they can fermentglucose, maltose, and cane sugar,forming equal amounts of alcohol andcarbonic acid gas, which causes theeffervescence of fermented andcarbonated drinks. There are, however,some types of yeasts found in milk andits products that are able to fermentmilk sugar.

All yeasts grow best in an acid

medium, hence those fermenting milksugar find suitable conditions forgrowth in sour milk or whey. They mayat times become of economicimportance in the cheese industry,because of the contamination of themilk with large numbers of them. Thearrangement of the whey vat is oftensuch that it cannot be completelyemptied and cleaned; the sour wheythus presents favorable conditions forthe growth of the lactose-fermentingyeasts. The return of the whey to thefarm in the milk can that is oftenimperfectly cleaned may serve tocontaminate the milk with the yeast. Inthe making of Swiss cheese the whey isoften so handled as to favor especially

the growth of such yeasts, and sincethis type of cheese is prepared fromsweet milk, the competition betweenthe yeast and the acid-forming bacteriais not so sharp as in the making ofcheddar cheese. The writers have foundseveral instances where considerableloss was occasioned in the Swisscheese industry through thedevelopment of gassy cheese due tothis type of fermentation.

The yeasty or alcoholic fermentationmay also be of importance in buttermaking. In many sections of thecountry the milk is separated on thefarm and the cream is forwarded to thecreamery at more or less infrequentintervals. It becomes sour and if it has

become contaminated with yeasts, theywill find favorable conditions forgrowth in the acid medium. A largeamount of carbon dioxide gas isproduced. Cans of gathered creamoften foam to such an extent as to runover, and in some cases actualexplosions have occurred on account ofthe great pressure caused by the gas.

Bitter fermentation of milk.Bitterness in milk may be due tobacteria that enter the milk after it isdrawn from the cow, or it may becaused by the feed consumed by theanimal. It has been previously shownthat certain specific substancescontained in the food may be absorbedand reappear in the milk. If the animal

eats ragweed, lupines, or other plantscontaining bitter substances, the milkis likely to have a bitter taste, whichwill be noticeable at the time the milkis drawn. The milk of cows at certainadvanced stages of lactation may showa bitter taste, due to a change in the ashconstituents of the milk in which thelime salts are largely replaced by saltsof sodium.

There are many bacteria that willimpart to milk a bitter taste. Milk thathas undergone the sweet-curdlingfermentation is likely to be bitter, as isthe ease with pasteurized milk. Someof the acid-forming bacteria are able todevelop a bitter principle, the milkretaining a pleasant odor and having

the normal amount of acid, while thetaste is intensely bitter. One of theauthors (H) found in the case of aWisconsin brick cheese factory, thatthe usual acid organism was almostwholly replaced by a bitter type.

Storage of milk at very lowtemperatures is conducive to theappearance of a bitter taste in milk, theexplanation in this case being that theacid-forming bacteria are unable togrow at a low temperature, while someof the putrefactive forms can multiplyand develop these astringent or bitterby-products.

Miscellaneous fermentations of milk.There are a number of other abnormal

fermentations in milk that occur sorarely as to be of but little economicimportance. Some, as the coloredmilks, are however, quite striking, andon this account have had muchattention directed to them in the past.There are bacteria that are able toproduce various colored substances,such as red, yellow, and blue. In casemilk becomes seeded with largenumbers of any of these kinds, it isvery likely to be colored by the growth.Red milk may be due to bacteria, butmore frequently is caused by the actualpresence of blood in the milk, due to awound in the udder, or the effect of asevere case of inflammation of thisgland. Such a condition may be readily

distinguished by allowing the milk tostand for a short time, in which case, ifdue to blood, the red corpuscles willsoon settle to the bottom of thecontainer, while bacterial troublesproducing a red coloration are moreevident on the surface.

It is also claimed that certain bacteriamay impart a soapy taste or turnipflavor to milk.

Cycle of fermentations in milk. If asample of milk is allowed to stand, itwill undergo a certain sequence offermentations that well illustrates theprinciple that one type of organisms isdependent on some other type tofurnish suitable conditions for its

development. This cycle of changesthat normally occurs in milk is asfollows: (1) The bacteria that comefrom the interior of the udder are thefirst to develop, but usually the changethey produce is not evident.

(2) Of the types that gain admission,subsequent to the milking, the acid-producing species are able to adjustthemselves most perfectly to theconditions that obtain in milk. Within afew hours they greatly predominate andsoon the milk curdles under theproduction of acid. Their growth,however, is soon stopped by theaccumulation of their own by-products.

(3) The semi-solid curdled milk, on

account of its acid reaction thenbecomes a favorable medium for thegrowth of molds; a prevalent form,known as Oidium lactis usuallydevelops as a white velvety layer. Themolds in their growth form alkaline by-products, which tend to neutralize theacid reaction, so that in the course oftwo to three weeks, if the layer of themilk is not too deep (an inch or less),the chemical reaction of the milkbecomes neutral or alkaline.

(4) The putrefactive bacteria whichfound their way into milk when it wasfirst drawn, and which have remaineddormant in the sour milk, now findfavorable conditions for growth. As aresult of their activity, the milk soon

undergoes a putrid decomposition,which is marked by offensive odors.

If the milk is placed under suchconditions as will exclude the growthof the mold, such as where the air isexcluded from the surface, the sourmilk will remain in that condition foran indefinite period, since theputrefactive bacteria are inhibited intheir development by the acid, in amanner comparable to the preservationof pickles in vinegar, or the keeping ofsilage because of the acid that isproduced as a result of the changes thatthe plant tissue undergoes whenexcluded from the air. The preservativeeffect of acids is of much importancein the case of certain dairy products

(see Chapter VIII).

Fermented drinks from milk. Withinthe last few years a great deal ofattention has been directed toward thepreparation of various kinds of drinksfrom milk. The use of such beverageshas rapidly increased. Butter milk isone which meets with the greatestapproval. The true butter milk fromcream that has been soured by thedesirable acid-forming bacteria has amild agreeable acid taste, wholly freefrom any sharpness that is often notedin butter milk made from cream inwhich considerable numbers of theundesirable acid-forming bacteria havegrown. Butter milk made frompasteurized cream soured with pure

cultures will have good keepingqualities and is a most healthful drinkfor all classes of people, even foryoung children.

Butter milk is also prepared byallowing milk to sour and thenbreaking up the curd by stirring. If thetype of fermentation is controlled asmay be done (see Chapter VII), such aform of fermented milk is a mostdesirable drink. It is probably ashealthful and has all the therapeuticproperties that are ascribed to otherforms of fermented milks such as theBulgarian "Yoghurt."

This type of fermented milk isproduced by an acid-forming organism

that can form large amounts of acid,2.0 or 3.0 per cent. The casein isdissolved to some extent and theremainder so changed, that it willremain in suspension for a long time ina finely divided form, after the curdhas been broken up. Such milk is soldunder various names at home andabroad. One of the authors (H) hasfound such organisms in practically allmilks examined. If raw milk is keptwarm (98° to 100° F.) in a stopperedbottle which is filled full, the aciditywill be found to increase slowly fromday to day, reaching a maximum in tento fourteen days. If the milk is thenexamined, it will be found to containlarge numbers of an acid-forming

organism very different in appearancefrom the bacteria causing the rapidsouring of milk at ordinarytemperatures. This organism is verysimilar if not identical with the onefound in the Bulgarian milk to whichthe name B. Bulgaricus has been given.The use of the milk fermented by thisorganism has spread rapidly because itis claimed by certain Europeanbacteriologists that it has a favorableeffect on the health of people,especially those suffering fromintestinal troubles. It is not at allcertain that ordinary sour milk orbutter milk will not have the sameeffect; in fact in many of the fermentedmilks sold in Europe, B. Bulgaricus has

not been found, but only the ordinarylactic acid bacteria.

Several alcoholic drinks made frommilk, such as kefir and koumiss, havebeen originated among the nomadictribes of Western Asia. Kefir isprepared from cow's milk by addingthe kefir ferment in the form of grainswhich contain a number of kinds ofbacteria and a yeast. The acid-formingbacteria impart a sour taste to thefermented milk, while the yeast formscarbon dioxide and about two per centof alcohol. If the milk is allowed toferment in stoppered bottles, theresulting product will be an acideffervescing drink, which is claimed tobe more easily digested than sweet

milk. This drink is used frequently inthe treatment of invalids but it isimprobable that it is more easilydigested than ordinary soured milk orbutter milk. The grains are removedfrom the fermented milk, and are thenadded to a quantity of fresh milk, orthey may be dried and kept for futureuse. When needed again, they aresoaked in water, then added to themilk.

Koumiss is made in Russia from mare'smilk and has much the samecomposition as kefir. In America andEurope it is made from cow's milk, byadding cane sugar and compressedyeast. The yeast ferments the canesugar while the acid-forming bacteria

ferment the milk sugar. There is thusobtained a drink that is similar incomposition to the real koumiss, inwhich both the acid and the alcoholcome from the fermentation of themilk sugar. In koumiss and kefir thecurd is very finely divided and willremain in suspension for a long time aswith butter milk.

Determination of the cause of taintsin milk. It is often of the greatestimportance to be able to locate thecause of abnormal odors or tastes inmilk, since methods for overcomingthe trouble can be intelligently appliedonly when the actual cause is known.An abnormal condition may be causedeither by the direct absorption of odors

before or after the milk is drawn fromthe animal, or it may be due tobacteria. If the milk appears bad-flavored when first drawn, and if suchtaint becomes less pronounced as themilk becomes older, it is likely that thetrouble is due to some characteristic ofthe feed. Certain feeds, like green rye,rape, cabbage, and certain of the rootcrops, like turnips, impart a strong odorto milk, if the same are fed shortlybefore milking. If the tainted conditionappears only some time after the milkis drawn, it may be due to the directabsorption of taints from thesurroundings in which the milk is kept,or it may be caused by bacteria. Thesecauses can often be differentiated, by

noting whether the taint tends toincrease in intensity with age. If such isthe case, it is likely that the cause is ofgerm origin, but if the reverse is true, itcannot be ascribed with certainty tobacteria and recourse must be had toother methods, such as the transfer of asmall quantity of the tainted milk to asample of perfectly fresh milk, orpreferably to some milk that has beenheated to the boiling point and thencooled. In the case of an odor due todirect physical absorption, it will notappear in the inoculated sample, sincethe small amount transferred is notsufficient to be noted. If it is due toliving organisms, the inoculation of thesmallest quantity into a fresh sample is

likely to reproduce the same change asoriginally noted.

Tests for the bacteriologicalcondition of milk. Within certainlimits milk can be indirectly examinedas to its bacterial content without anyspecial equipment. Milk when drawnfrom the cow has an apparent acidityranging from 0.16 to 0.18 per cent. Bythe use of any of the methods ofdetermining acidity in milk, much canbe told concerning the number ofbacteria in the milk, and henceconcerning its keeping quality. Milkthat has an acidity of over 0.2 per centis certain to contain many bacteria, andconsequently will keep poorly. Suchmilk is of low value for market milk,

but may not be objectionable for butteror cheese making. If the acidity isbelow 0.2 per cent, but little can be toldas to the numbers of bacteria, since anyincrease in acid is always preceded byan enormous increase in the numbersof acid-forming bacteria.

A more important test than the acidtest, from the standpoint of the butterand cheese maker, and even the milkdealer, is the fermentation test. In itssimplest form, it consists in placing asample of the milk to be tested in awarm place and noting the timerequired to curdle and the type of curdformed. In this country thefermentation test has been largelysupplanted by the Wisconsin curd test

which possesses the advantage ofdetecting the presence of bacteriaharmful in cheese making, especiallythe gas forming bacteria.

The curd test is helpful in detecting thesource of an abnormal condition in amilk supply coming from diversesources. The milk furnished by eachpatron can be tested separately and thetrouble located, perhaps in anindividual herd; the offending herddetermined, the test may then be usedon the milk of individual cows. Thecheese maker and the milk dealershould be able not only to detect whichof the patrons furnish him poor milk,but he should be able to give the patrondefinite instructions how to avoid the

sources of such trouble. Thisinformation can be given only when thesource is positively known.

FIG. 23.—CURD TEST.A good curd obtained from milk

containing no harmful bacteria butmany desirable acid-forming

organisms.

The Wisconsin curd test is made asfollows: Samples of the milk to betested are placed in sterile pint fruitjars. The milk is warmed to 90° F., tendrops of rennet are added to eachsample, and as soon as the curd issolid, it is cut into small pieces with acase knife so as to facilitate theexpulsion of the whey. As the curdsettles to the bottom of the vessel, thewhey is poured off at intervals so that apat of firm curd is left. As the milkcurdles the bacteria are enmeshed andare carried with the curd. The jars arekept at a temperature of 100° to 105°F., since this temperature is favorableto growth of the bacteria that are

sought, the gas-forming organisms. Atthe end of ten to twelve hours, the jarsare examined; if the curd is solid, thetexture firm, not mushy or slimy on thesurface, if the odor is agreeable, itindicates that the milk contains few ornone of the undesirable forms ofbacteria. If the curd is full of gas holes,it is apparent that undesirable bacteriaare present and under suchcircumstances the curd will not have anagreeable odor. If the gas-formingbacteria are numerous, the curd mayeven be spongy from the abundance ofgas holes, and the undesirable odormore pronounced. Such curds are toughand rubbery. In some cases a bad flavoror odor is apparent even though the

texture of the curd is not open and fullof holes. The curd, the surface of whichis slimy indicates undesirableorganisms. A solid curd of agreeableodor is indicative of the presence of thedesirable acid-forming bacteria. Such amilk is excellent from the standpoint ofthe butter or cheese maker, but may notbe so desirable from the standpoint ofthe milk dealer on account of its poorkeeping qualities. On the other hand amilk suitable from the standpoint ofthe milk dealer, on account of its lowgerm content, and hence good keepingquality, may give a poor curd test. It iscertain to contain some bacteria,especially those from the interior of theudder while it may contain none of the

desirable acid-forming organismswithout which a curd of good textureand flavor can not be obtained. Thebacteria in the clean milk will growrapidly at the high temperatures atwhich the curds are kept and thechanges they will produce as to flavorand odor may be undesirable. The milkmight be judged as poor when in realityit might be a most excellent sample,and if kept at the ordinary storagetemperatures, it might keep for days.The test when used for market milkshould be interpreted with this in mind.

FIG. 24.—CURD TEST.The curd obtained from milkcontaining many gas-forming

bacteria. The irregular, angularholes are mechanical, due to the

imperfect fusion of the pieces ofcurd.

If the results are to be of any value, thetest must be made with care to avoidall sources of error; the tester mustknow that the bacteria causing the gasand bad flavors in the sample wereoriginally present in the milk at thetime the sample was taken, and thatthey have not come from the containersused or from other sources. To insurethese conditions the jars must bethoroughly cleaned and then sterilizedjust before use by placing them in coldwater and bringing them to the boilingpoint, or sterilized by a thoroughsteaming. The sample of milk of apatron must be taken so as to avoid

contamination from the milk of theother patrons. This can best be done byfilling the jars as the milk is pouredfrom the patron's can into the weighcan. In cutting the curds, the knife usedmust be dipped in hot water betweeneach test to cleanse the same. In short,the test should be carried out with greatcare so that the tester is certain of theresults obtained.

Other tests for the bacteriologicalcondition of milk will be described inChapter IX.

Overcoming abnormalfermentations. The lactic acid bacteriaare often looked upon as normal tomilk, and it is certain that they are to

be classed as harmful, only as theyinjure the keeping qualities of milk. Inmilk designed for butter and cheesetheir presence is necessary. At timesthese desirable forms of bacteria maydisappear, and be replaced by lessdesirable types. In one case it wasobserved that the usual lactic bacteriahad been replaced in a cheese factorysupply by an acid-forming organismthat produced an intensely bitter tastein the milk, thus rendering the cheeseof no value. When such harmful formsappear, they must be overcome, and thenormal types of bacteria replaced. Athorough cleaning of the milk utensils,attention to the cattle and all placesfrom which such bacteria may find

their way into the milk is oftensufficient to cause a disappearance ofthe trouble. If the acid-formingbacteria have disappeared, theinoculation of the milk with cultures inways later to be discussed is often ofadvantage. At times more stringentmeasures must be employed in order todestroy the harmful bacteria, such asthe use of strong disinfectants.

Disinfection and disinfectants. If anybuilding or room becomes infectedwith disease-producing bacteria, or iforganisms causing abnormalfermentations become established in afactory, the use of a disinfectant thatwill destroy with great rapidity the lifeof bacteria is necessary. The

disinfection of all types of dairyapparatus and utensils can beaccomplished by thorough cleansing,and by the use of steam or boilingwater. The disinfection of rooms andstables cannot be so readilyaccomplished.

Consideration must always be given tothe resistance of the organism it isdesired to destroy. Those that formspores are very resistant toward allchemical agents, while those that donot produce these resistant bodies areeasily killed. In the dairy and factory, itis often necessary to destroy theorganisms that develop in decomposingorganic matter. Here, as in alldisinfection, a thorough cleaning

should precede the application of anydisinfectant. Some chemicals act asdeodorants, i.e., destroy the offensiveodor, without removing the cause. It isimpossible effectually to destroybacteria embedded in a mass of organicmatter, and through the removal of thematerial itself, the larger part of thebacteria will be removed. Thedisinfectant then comes in directcontact with the surface to bedisinfected, consequently destroys thebacteria not removed in the cleaning.

All places in which dairy work of anykind is done should be provided withan abundance of light and air. Thedirect rays of the sun have a powerfuldisinfecting action, and light makes

evident accumulations of dirt that in adarker room would be unnoticed.Ventilation keeps the rooms dry andthus prevents the growth of mold andthe development of a musty odor.

Disinfectants are divided into twoclasses: (1) solid materials used insuspension, or in watery solutions; (2)gaseous substances. The latter arepreferable for room disinfection whentheir use is permissible, for the gaspenetrates to every part of the space,even into the cracks. Gaseousdisinfectants can only be used when thespace is tightly closed, for the gas mustbe confined for several hours in theroom, in order to make the processeffective. Such disinfectants can often

be used to advantage in the treatmentof refrigerators and cheese rooms todestroy mold spores. In less tightlyclosed spaces, reliance must be placedon the use of the solid or liquiddisinfectants.

Lime. Quick lime or stone lime has aconsiderable disinfecting action. Onexposure to the air, quick limebecomes air slaked, and then has nodisinfecting action whatever. Water-slaked lime used in the form of whitewash, lime water, or the powder iseffective. Air-slaked and water-slakedlime are similar in appearance, but adifference can be noted by placing aparticle of each on the tongue; the air-slaked tastes like chalk while the

water-slaked material causes thetongue to burn.

White wash is one of the most effectiveagents that can be used in thedisinfection of barns, milkrooms, etc.Besides being a fairly strongdisinfectant, it has a tendency to absorbodor, it encrusts the walls and lightensthe interior of rooms. It can be appliedwith a brush or with a spray pump.

Carbolic acid and cresol compounds.These substances are among thecheapest and best disinfectants, buttheir use in the dairy is not advisable,on account of the penetrating andlasting odor. They can be used toadvantage on the farm. Some of the

proprietary compounds, as Zenoleum,Kresol, etc., are easily applied, sincethey mix readily with water in allproportions, forming a milky-whiteemulsion that can be easily applied.They are less caustic and lesspoisonous than carbolic acid.

Corrosive sublimate. Corrosivesublimate is the most efficientdisinfectant under ordinary conditions.It is such an intense poison that it mustbe used with caution in places to whichstock have access, or in the dairy. Asolution of one part of the salt to athousand parts of water (half ounce to 4gallons of water) is the standardgenerally used.

For gutters, drains, and waste pipes infactories, ferrous sulphate (greenvitriol), and copper sulphate (bluevitriol), can be used to advantage. Theyare to be classed as deodorants ratherthan as true disinfectants. Since theyhave no odor of their own, they can beused in any amount in the dairy.

Sulphur can be used to advantage inthe destruction of mold spores incheese rooms, but the effect of thevapors of burning sulphur on germ lifeis relatively slight, unless there is anabundant supply of moisture in the airof the enclosed space, in which casesulphurous acid is formed which has amuch greater effect. To have thedesired effect sulphur should be burned

at the rate of three pounds to each onethousand cubic feet of space, and theroom kept sealed for at least twelvehours. If the sulphur is placed in aniron kettle which is set in a vessel ofwater, danger from fire will beavoided, and the heat generated by theburning sulphur will evaporatesufficient water to increase the effectof the fumes.

Formalin. Another disinfectant thatmay be used as a liquid or as a gas isformalin, which is a watery solution ofthe gas, formaldehyde. It is much morepowerful in its action than sulphur, andhas a great advantage over corrosivesublimate and other strongdisinfectants in that it is not so

poisonous to animals as it is to bacteriaand fungi.

It can be used as a solution (one to fiveper cent) for the washing of woodwork,or for the treatment of any object, sinceit has no corrosive action. It can also beemployed as a gaseous disinfectant forthe treatment of rooms. It is mostconveniently applied by suspendinglarge cloths in the room and sprayingthem with the solution, then closing theroom for a number of hours.

Bleaching powder. Chloride of lime,or bleaching powder as it is oftencalled, is a good disinfectant, as well asa deodorant. It is used as a wash in theproportion of four to six ounces to a

gallon of water. It must be used withcare in factories since the free chlorinethat is given off has a penetrating odor.

CHAPTER VI.

PRESERVATION OFMILK.

It has been shown in a previous chapterthat milk becomes contaminated with amultitude of bacteria not only on thefarm where it is produced, but duringthe various stages prior to its use.Many of the bacteria which find theirway into milk are readily able todevelop, and by their growth, renderthe milk unfit, or even harmful forhuman food. With the most stringent

precautions that can reasonably betaken, it is impossible to avoid allcontamination; hence, all grades ofmilk will soon spoil, unless somemeans of preservation is employed.Indeed, of all the foods classed asperishable, milk is the one that mostrapidly deteriorates. Produced underordinary conditions, it is unfit forordinary use in a few hours if kept at70° F.

There are three possible ways by whichmilk may be preserved: (1) Theremoval of bacteria that have gainedentrance to it; (2) The prevention ofgrowth of the contained bacteria; (3)The destruction of the containedorganisms. In practice at least two and

sometimes all of these methods areemployed. The prevention ofcontamination, a subject discussed inChapter III is in reality one of the mostefficient means of preserving milk. Inmilk production, as elsewhere,prevention is preferable to cure. Milkproduced under such conditions that itsgerm content is but a few thousand percubic centimeter will keep much longerthan that handled in the ordinarymanner.

It might naturally be supposed that anymethod by which dirt is removed frommilk would improve the keepingquality of milk, due to the reduction ofbacteria, yet while the straining of themilk at the time of milking removes

dirt of various kinds, it does notappreciably enhance the keepingquality, owing to the fact that thebacteria adherent to the dirt particlesare washed off in straining, and passthrough the pores of the strainer.

Filtration of milk. It is possible toremove all bacteria from water andother fluids and thus render themsterile by passing through filters ofunglazed porcelain. This process cannot be used with milk for the fatglobules are larger than the bacteria(see Fig. 6) and any process that wouldremove the latter would also removethe former. The term "filtration" isapplied to a process used in someEuropean cities for the removal of the

insoluble dirt that has been introducedinto the milk. Suitable containers arefilled with layers of coarse sand at thebottom and with finer sand at the top.The milk is introduced at the bottomand is forced upward through the sand.Such a filtering process is a veryefficient means of removing the dirt;but unless the filters are keptscrupulously clean, the bacteria arelikely to grow in the filtering material,so that the number of organisms in themilk may actually be increased by thefiltering process. It is necessary toremove the sand daily and thoroughlywash and sterilize the same. The extracare required in keeping these sandfilters in sanitary condition has been

the great objection to their employmentin this country. Filters of other materialsuch as cellulose have been employedbut with no marked success.

Clarifying milk. A much moreefficient and less troublesome meansof removing the insoluble foreignparticles from milk is to pass it througha cream separator, allowing the creamand skim milk to mix in the samecontainer. The slime that collects onthe wall of the separator bowl is madeup of dirt, casein, bacteria, and thecellular debris from the interior of theudder. The bacteria are heavier than themilk serum, and would, therefore, bedeposited on the wall of the bowl wereit not for other factors that in a

measure prevent this. The movement ofthe fat toward the center of the bowlcarries into the cream a considerableproportion of the bacteria in the milk.The slime will always contain manymore bacteria than the milk, but the percent of bacteria thus removed isrelatively low, due to the small amountof slime obtained from the milk, sothat the actual effect of clarification onthe keeping quality of milk isinsignificant. The complete removal ofall insoluble and therefore visible dirtis, however, regarded of sufficientvalue to warrant the use.

Machines designed especially for theclarification of milk are now widelyused. They differ from the cream

separator in that the milk is introducedat the outside of the bowl and hencethere is no separation of the fat fromthe serum. It is claimed that theremoval of the dirt, cells from theinterior of the udder and bacteria is asefficiently done as when the separatoris used. The advantages claimed for themachine are that it has no effect on thesubsequent gravity creaming of themilk and that less power is demandedthan for the separator.

From the standpoint of the consumer,all processes by which dirt is removedfrom milk are objectionable, since theymake the milk appear cleaner andbetter than it really is, the harm havingbeen done when the dirt with the

adherent bacteria found its way into themilk. The removal of the foreignmatter that has been introduced into themilk will have but little effect inreducing the number of bacteria, sincea large part of the organisms will havebeen washed off the insoluble material.All of these processes improve theappearance of the milk but have littleor no influence in increasing itskeeping quality or its healthfulness.

Preservation by cold. The onlylegitimate way of preventing thegrowth of bacteria in milk is byholding it at temperatures at which theordinary forms of bacteria cannotthrive. Bacterial growth is greatlychecked at temperatures approximating

50° F., or below, although certain typesmultiply at the freezing point orslightly above. If food products areactually congealed, no germ growthoccurs, and they may be kept quiteindefinitely, but this process cannot besuccessfully applied to milk, as the fatand casein are physically changed, sothat a normal emulsion can not againbe made when the frozen milk ismelted. The fat separates in visiblemasses as though the milk had beenpartially churned. On account of thisfact milk must be stored attemperatures above the freezing point.In Denmark efforts have been made topreserve milk, that is to be shippedlong distances, by freezing a portion of

the milk, and placing a block of thefrozen milk in each can after coolingthe main mass of milk nearly to thefreezing point. Even this method hasnot proven practical, and at presentreliance is placed on thorough chillingof the milk. At 32° F., the lacticbacteria cannot grow, but other types,such as certain of the putrefactiveforms grow slowly; the milk may,therefore, have no objectionable odoror taste and yet be swarming withbacteria. In cities the practice isfollowed of placing cream in cold-storage during the cooler periods ofsummer in preparation for an increaseddemand, during hot weather or onholidays. It seems probable that

poisoning from ice cream may, attimes, be due to the use of such cream.

Preservation by the use ofantiseptics. Many chemical substancesprevent the growth of bacteria whenadded to food supplies; such substancesthus used are called preservatives. Inthe past some of these have been usedin milk to a great extent, but at present,on account of stringent pure food laws,they are employed only to a slightextent. There is a great temptation forthe small milk dealer in the city toemploy them to preserve the excess ofmilk from day to day, as through theuse of a few cents worth of somepreparation, many dollars worth ofmilk may be kept from spoiling until it

can be sold to the unsuspectingconsumer.

Formalin has been most widely used inmilk because it is a most efficientpreservative; it is cheap and cannot bedetected by the consumer, although itinjures the digestibility of the casein.One ounce will keep one thousandpounds of milk sweet for twenty-fourto forty-eight hours. Borax, boric acid,and salicylic acid have also been used,but these substances must be employedin much larger quantities thanformalin. Bicarbonate of soda hassometimes been used although it is nota true preservative. Its effect is basedupon the neutralization of the acidproduced by bacterial growth. The

treated milk does not taste sour soquickly, and the curdling of the milk isalso delayed.

Many proprietary compounds for milkpreservation have been placed on themarket in the past, but the use of all ofthese is illegal in most states. Thefederal law also prohibits their use inall dairy products that pass intointerstate commerce.

Within recent years a method for thepreservation of milk was introduced bya Danish engineer, Budde, whichconsists of adding to milk a very smallamount of peroxid of hydrogen whichis a very efficient antiseptic. Theperoxid is decomposed by some

substance in the milk; the products ofdecomposition being water and freeoxygen. The peroxid together with theapplication of heat at a comparativelylow temperature (122° F.) is sufficientto destroy the larger part of the bacteriain the milk. Practical difficulties areencountered in the commercialapplication, so that it is probable theprocess will never be a commercialsuccess.

For the preservation of compositesamples of milk for analyticalpurposes, such as the Babcock test,strong disinfectants, as corrosivesublimate, are employed. This materialis very poisonous, and leaves the milkunchanged in appearance. Some

coloring matter is therefore usuallymixed with the sublimate in makingthe preservative tablets, so as to rendertheir use more conspicuous. Corrosivesublimate not only stops all bacterialgrowth, but quickly destroys the life ofthe cells. Bichromate of potash isgenerally employed in the preservationof composite samples for the Hartcasein test.

Destruction of bacteria in milk.Actual destruction of the life ofbacterial cells by heat is one of themost important ways for preservingmilk. Heat easily destroys thevegetating, growing bacteria, while thespores, of which there are always anumber in milk, are very resistant. If,

however, the growing organisms aredestroyed, the milk will keep muchlonger than if it had not been sotreated.

The process of pasteurization was firstused by the French bacteriologist,Pasteur, for the treatment of the winesof his native district which were likelyto undergo undesirable types offermentations due to bacteria. From thewine industry it was applied in thebrewing industry, and was later foundto be of the greatest service in the dairyindustry. The process of pasteurizationmay be briefly defined, as the heatingof milk to temperatures, varying from140° F. and upward for a longer orshorter time, and subsequently cooling

to a low temperature, so as to preventthe germination of the spores that arenot destroyed by the heating.

Effect of heat on milk. When milk isheated it undergoes more or lessprofound changes, depending on thetemperature and time of heating. Someof these changes are of practicalimportance, since they are more or lessevident, and objectionable to theconsumer.

In raw milk the fat globules are largelyfound in larger or smaller aggregates,rather than uniformly distributedthroughout the serum. The surface of amass of fat globules is smaller inproportion to the volume of the mass

than is the case with single globules,hence globule clusters encounter lessresistance in their passage through theserum, either as they rise to the surfacein gravity creaming, or in the separatorbowl. If these clusters are broken up, sothat the globules are uniformlydistributed, the milk will cream muchless rapidly and completely. In theprocess known as "homogenization" ofmilk, the individual fat globules arebroken into such small globules, thatthey cannot overcome the viscosity ofthe serum, and they remain distributedthroughout the milk. In such cases, nocream rises, and even the creamseparator is unable to remove the fatfrom such milk.

In selling bottled milk, it is highlydesirable that the cream line shouldshow distinctly. In normal milk, thisline forms in a few hours, but wheremilk is heated to a high temperature,and agitated at the same time, theclusters of fat globules are broken apartand the creaming power injured. Thisphysical change is dependent not onlyon the temperature, but also on thetime of exposure. A momentaryexposure at 160° F., or for 20 minutesat 145° F., is about the maximum limitwhich can be applied to milk withoutmaterial injury to the creamingproperty.

FIG. 25.—FAT GLOBULES IN RAW MILK.In raw milk the fat globules are in

masses of varying sizes. These rise tothe surface quickly in gravity

creaming.

The body or consistency of pasteurizedcream may be restored by allowing thecream to stand for several days at lowtemperatures, or by the addition of asmall amount of sucrate of lime. This

substance, known to the dairy trade as"viscogen," is made by adding to athick solution of cane sugar, somefreshly slaked lime. The sugar solutionpermits of the dissolving of a muchlarger amount of the lime than ispossible in water. When the liquid isallowed to settle, the clear solution isthen decanted off and is used at the rateof about one part to 100 to 150 parts ofcream. The fat globules are, by itsaction, brought into aggregates and thebody of the cream thus restored.Viscogen contains nothing that is at allharmful, but milk and cream to whichit is added must be sold under somedistinctive name as "visco-cream,"since the laws of practically all states

do not allow the addition of anysubstance whatever to milk or cream.

FIG. 26.—FAT GLOBULES IN HEATED MILK.

When milk is heated the masses ofglobules are broken up and fat

globules are uniformly distributedthroughout the milk.

FIG. 27.—CREAMING OF MILK.

The cylinder on the left contains rawmilk; that in the center, milk heatedto 140° F. for twenty minutes; on the

right, milk heated to 160° F. fortwenty minutes. The dark line

indicates the depth of the cream aftertwenty-four hours. The breaking up

of the fat globule clusters delaysgreatly the rising of the cream.

Heated milk has a taste unlike that ofraw milk; to one not accustomed to itthe taste is objectionable. This changeis due to some extent to the expulsionof the carbon dioxide from the milk.The insipid taste of boiled water is, inpart, due to its freedom from carbondioxide. The production of this cooked

flavor is dependent upon the time andtemperature of exposure. It has beenclaimed that heated milk is lessdigestible than raw, and a considerableamount of experimental work has beendone, both on animals and children, inorder to determine the relativedigestibility of heated and raw milk.The results obtained have beencontradictory. It is claimed that heatedmilk causes such diseases as rickets,scurvy and marasmus in children. It isprobably true that milk heated to theboiling point is less fitted as food forthe young child than raw milk, but, onthe other hand, it has not been proventhat properly pasteurized milk is anunsuitable food for children. The best

evidence has been accumulated inrecent years, in many of the large citiesof this country and of Europe, wherepasteurized milk has been used withthe greatest success in the feeding ofchildren of all ages.

The heated milk does not curdle readilywhen rennet is added due to theprecipitation of the lime salts by heat.The curdling power can be restored bythe addition of soluble lime salts or ofacids.

Purpose of pasteurization. There aretwo reasons for the pasteurization ofmilk: (1) To improve the keepingquality; (2) To destroy any pathogenicbacteria it may contain. The first may

be called the economic reason; thesecond, the hygienic reason furpasteurization. In the selection of aproper pasteurizing temperature, twofactors must be taken into account:First, the effect of heat on milk, andsecond, the temperature necessary todestroy those forms of bacteria that areof the greatest importance, as far as thekeeping properties are concerned, andthe pathogenic bacteria that mightpossibly be present in the milk. Thelactic acid bacteria are non-spore-bearing and are not resistant to heat.Most of them are destroyed when themilk is heated to 140° F. for fifteenminutes or to 160° F. for a moment. Toinsure proper keeping quality,

somewhat higher temperatures must beemployed, such as 145° to 150° F. forfifteen to twenty minutes.

Milk pasteurized at these temperatureswill, as a rule, undergo an acidfermentation in much the same manneras will raw milk. The rate with whichthe acid develops is of course muchslower than in the raw milk, due to thedestruction of 95 to 99 per cent of theacid-forming bacteria. If the milk hasbeen pasteurized at highertemperatures, the acid fermentationmay not appear. The spores of thespore-bearing organisms will be left;these may germinate and cause theircharacteristic change in milk, which, aspreviously noted, is usually a sweet-

curdling or a digesting fermentation.Since the changes they produce in themilk are not evident at first, it might beused as food even though it was so faradvanced in decomposition as to beundesirable or even harmful as food.Indeed one of the objections urgedagainst pasteurization is that it destroysthe natural safe guard, the acid-formingbacteria. Many people are soaccustomed to use this as the indicationof spoiled milk that they will use milklong after it should be used if it doesnot show an acid fermentation.

The butyric acid organisms are sporeforming and may at times produce theircharacteristic fermentation inpasteurized milk. The milk shows gas

formation and develops anobjectionable odor.

The pathogenic bacteria most likely tobe present in the milk are the typhoidand the tubercle organisms. Thetyphoid bacillus is no more resistant toheat than the ordinary acid-formingbacteria, and all milk that has beenheated, so as to impart to it satisfactorykeeping properties, will certainly befree from typhoid bacilli. It hassometimes been asserted that thetubercle bacillus is very resistant toheat; some claiming that it is necessaryto heat milk to 200° F. in order todestroy it. Other experimenters haveasserted that lower temperatures wouldsuffice, but the temperatures were still

above those at which the milk isphysically and chemically changed bythe heating process. More recent workhas shown that not all sources of errorwere avoided in the earlier attempts todetermine the thermal death point ofthe tubercle bacillus, as, for example, ithas been shown by the authors that the"scalded film" that forms on thesurface of milk when heated in an openvessel will protect the bacteriaimbedded in it. It has also been shownby the authors that a temperature of140° F., for twenty minutes or 160° F.for one minute will destroy the tuberclebacilli in milk, in case the heating isdone with sufficient thoroughness toinsure all particles of the milk being

heated to the same temperature forthese periods of time.

The pasteurization of milk can be donein such a manner as to impart to it goodkeeping qualities and to insure itsfreedom from pathogenic bacteria, andyet not impair its physical andchemical properties, but much of theso-called pasteurized milk placed onthe market is not treated in accordancewith proper hygienic methods.

FIG. 28.—THE POTT'S DISCONTINUOUS

PASTEURIZER.

The milk is placed in the innercompartment. For heating and

cooling, hot or cold water is passedbetween the jackets.

Methods of pasteurization. In order todestroy the bacteria in milk, it isnecessary that the milk be heated for avarying time dependent upon the

temperature employed. A lowertemperature for a considerable periodmay exert the same effect on thebacteria as a higher temperature for ashorter time. In practice, two types ofpasteurizing machines are employed,depending on the temperature at whichthe milk is to be treated. Thediscontinuous machines orintermittently operated pasteurizers arethose in which the milk is heated forany desired time at any temperature.Such machines consist of jacketedcontainers the inner receptacle beingfilled with milk, while the outer spacebetween the walls is filled withcirculating hot water or steam. Themilk is kept agitated by the rotation of

the machine. After it is heated, it iscooled in the same container byreplacing the hot water first with coldwater, then ice water. The disadvantageof this process is that the capacity ofthe machine is limited which precludesits use in places where large quantitiesof milk or cream are handled; for thepasteurization of limited quantities, itis very successful, as every particle ofmilk or cream is under the directcontrol of the operator and may bethoroughly and efficiently treated.

As pasteurization was introduced forthe treatment of market milk, and forthe preparation of cream for butter,machines have been devised whichpermit large quantities, as thousands of

pounds, to be handled per hour. It isevident under these conditions that themilk must be heated for only a shorttime, and hence a higher temperaturemust be employed. These machines arecalled "continuous flow" pasteurizerssince the milk passes through them in aconstant stream. The period ofexposure is very short, in some only afew seconds; hence, they aresometimes called "flash" pasteurizers.

FIG. 29.—A CONTINUOUS PASTEURIZER.

The milk is exposed but a short timesince it flows through the heater in a

constant stream.

All machines of this type possess theobvious disadvantage that it isimpossible to heat all of the milk for auniform period. The milk in contactwith the walls of the machine flowsmuch more slowly than in the middleof the stream, just as the current nearthe bank is less rapid than in mid-stream. In none of the machines yetdevised have the designers been able toovercome this disadvantage. In a test ofone of the most widely usedpasteurizers of this type, it was foundthat some of the milk passed through

the machine in 15 seconds, while thelarger part of it was held for about 30seconds, and some as long as forty-fiveto sixty seconds. If the temperatureemployed had been such as to destroythe bacteria in that part of the milkheated for the minimum time, hygienicsafety would be assured, but in order toavoid injuring the physical propertiesof the milk, the tendency is to use aslow a temperature as possible, so thatthe milk heated for the minimum timemay often contain organisms that havepassed through the machine uninjured.

Many devices have been proposed forthe heating and cooling of the milk. Inmany of the pasteurizers, the milkflows in a thin stream over a metal

surface, on the opposite side of whichis the heating agent, usually steam;while in others, the milk is allowed toflow through a vat in which revolve aseries of discs into which steam ispassed. The discs are of considerablesize; thus, making a large heatingsurface; the milk is thus heatedquickly, and is constantly stirred by therotation of the heating discs. In othertypes the milk passes into the bottomof a chamber in which a dasherrevolves at a rapid rate. This catchesthe milk, throwing it in a thin film ontothe wall of the chamber, which isheated with steam on the opposite side.From such machines, of which theFjord, the Jensen, and the Reid

machines are types, the milk may beforced to a considerable height. Theseare widely used in this country for thepasteurization of milk and cream forbutter making.

Milk that has been heated must becooled at once by the use of cold waterand ice. In order to economize in theuse of both steam and cooling agents,the so-called regenerative machineswere devised. The essential feature ofthese machines lies in the fact that thecold milk inlet and the hot milk outletare on opposite sides of a singlepartition; thus the inflowing cold milkis partially heated by means of thealready treated hot milk which it isdesired to cool.

In order to avoid the disadvantages ofthe continuous machines, viz., lack ofcontrol, an apparatus has recently beendevised which can handle largequantities of milk, heating the same toany temperature for any desired time.In such a machine the milk is firstheated in a continuous heater, and isthen passed into large tanks in which itis allowed to remain for the desiredtime, and from which it flows over thecoolers. Such an apparatus is called a"holding" machine, and is probably themost feasible type of pasteurizer nowon the market, when all factors areconsidered. In some of the continuousmachines, an attempt is made toaccomplish the same result, by

building the machine so that the milkrequires fifteen to twenty minutes forpassage through the machine, but in allsuch cases the same disadvantage ofvariation in rate of flow, as in othercontinuous flow type of machinesobtains.

Tests of pasteurizing machines. It ispossible for the operator to test the rateof flow in a machine, so as todetermine whether all of the milk isheated for a uniform time. This is donemost easily in the following manner:The machine is first filled with water,heating the same to the desiredtemperature, and regulating the rate offlow as it would be if milk was used.The flow of water is then turned off,

and a stream of milk containing aknown per cent of fat admitted to themachine. The time elapsing betweenthe admission of milk to the machine,and that at which the first sign ofturbidity is noted at the outlet, will bethe minimum period necessary for anyportion of the milk to flow through themachine. At frequent intervalsthereafter, samples of the outflowingliquid may be collected, noting thetime at which each sample is taken.The percentage of fat in the varioussamples is determined by the Babcocktest; at the moment when all of thewater has been removed, the sampletaken will show the same fat content asthe milk used. The samples taken

previous to this will show a lower fattest, dependent upon the relativeamount of water and milk. In thismanner, the minimum, the maximum,and the average period of exposure ofmilk in the machine tested, can bedetermined with exactness.

The accompanying table gives resultsthat were obtained in the testing of oneof the continuous types of machines.The machine in question required aboutthree hundred pounds of milk to fill itand was supposed to handle 1,000pounds per hour. Thus theoretically itshould require twenty minutes for anyportion of the milk to pass through themachine. As will be seen from the data,some of the milk passed through within

seven minutes after the water was shutoff and the milk turned on. The figuresalso show that not all of the water hadbeen replaced by the milk in even 45minutes. In actual practice like resultswill be obtained, and a portion of themilk will be heated to the temperatureemployed but a short time. In this, thevegetating bacteria will not be whollydestroyed.

Trial

Percentoffatin

milk

Per cent of fat in milkcoming from machine

at following timesMINUTES

7 11 15 19 23 27 36 47No. 4.0

I 0.2 0.8 1.6 2.0 2.4 2.6No.II 3.8 0.2 0.6 1.5 1.8 2.2 2.6 3.0 3.4No.III 3.5

0.7 1.9 2.4 2.8 2.8 3.0 3.4 3.4

Pasteurization of small quantities ofmilk. It is often desirable to treat asmall quantity of milk for home use, inwhich case the commercial types ofpasteurizers are out of the question.This treatment can be done in a numberof ways, consideration always beingpaid to the manner of heating whichshould be done under such conditions,as have been shown to be necessary forefficient pasteurization. Milk may beheated in tall, narrow cans which are

placed in hot water. In the household,milk may be treated by placing thefilled bottle in a pail having a falsebottom so the bottle shall not be brokenwhen the pail is placed on the stove.The pail should be filled with water sothat its level is about the same as thatof the milk. The water is then heated tothe desired temperature, maintained forthe requisite period of time, and is thencooled as rapidly as possible. Duringthe heating, the mouth of the bottleshould be covered, either with aninverted glass tumbler, or the paper capmay be left in place, simply punching asmall hole through it so as to permit ofthe insertion of a thermometer.

FIG. 30.—A PASTEURIZER FOR USE IN THE

HOME.

A milk bottle with a tumbler for acover. The cover prevents the

formation of the "scalded layer" onthe milk during the heating and alsoprotects the mouth of the bottle from

dust.

Efficiency of pasteurizing. It is easyto destroy over 99 per cent of thebacteria present by the use of any ofthe modern types of machines. Thenumber remaining after treatment willbe largely dependent, other thingsbeing equal, upon the number ofbacteria before pasteurization. Thepasteurizing process is not one bywhich poor milk can be changed intogood milk, nor is it legitimate to usethe process in place of cleanliness, as issometimes done. There is a legitimatefield for the process in the handling of

market milk, as well as in thecreamery; but it should be used toimprove the keeping quality, and toinsure the freedom of the milk frompathogenic bacteria, when otherprotective measures have been carriedas far as possible under the prevailingconditions.

Details of process. If the process is tobe successful, due attention must begiven to certain details. In thetreatment of market milk, care shouldbe taken to use only that in which theacidity has not materially increased. Afair standard is about 0.2 per cent. Highacid milk usually means old milk ordirty milk, either of which is verylikely to contain many more spore-

bearing bacteria than clean, fresh milk.The greater the number of spores, themore rapidly will the pasteurized milkspoil. If it is possible to exercise anyselection of milk prior topasteurization, the rapid test fordetermination of acidity will prove ofgreat advantage.

Care should be taken to preventfluctuations in the temperature towhich the milk is heated. With varyingsteam pressure and variations in therate of flow of milk, these fluctuationsmay be very considerable. Regulatorsare now made that will control thetemperature within narrow limits.

In all pasteurized milk as it flows from

the machine, there will remain someliving bacteria. The spores will not bedestroyed by any pasteurizing process,and under commercial conditions,vegetating bacteria are also present. Ifthe milk is not quickly chilled afterheating, these forms will grow, andtheir development is particularlyhastened by the destruction of thelactic bacteria, the acid of which wouldotherwise hold them in check. Theresult is that, unless immediatelychilled, pasteurized milk spoils almostas rapidly as though it had not beenheated at all. Efficient and rapidcooling are, therefore, as essential aportion of the process as the heatingitself.

Care should also be taken to protect themilk from contamination aftertreatment. Every utensil with which itcomes in contact should be sterilized.The bottles should be thoroughlywashed and sterilized and subsequentlyprotected from dust until used.

Sterilization of milk. It is possible torender milk sterile by the use oftemperatures above the boiling point ofwater, where it is heated in a closedvessel, in which steam under pressureis generated. Such milk is often foundin the European markets. In our owncountry, the only milk of this kind isthe so-called "evaporated milk." In thisprocess sweet fresh milk is evaporatedin vacuum pans to about one-third of

the original volume. This is then placedin tin cans, which are treated, as in thecanning of such vegetables as peas andcorn, by heating the milk to 230° or240° F. for a few minutes. In thisprocess, the bacteria (spores as well asvegetating forms) are completelykilled, and the milk acquires abrownish tint, due to thecaramelization of the sugar. Theappearance of the product is verysimilar to cream, and previous to thepassage of the pure food law, it wassold as evaporated cream.

Condensed milk is not wholly freefrom bacteria, but is sufficiently thick,by reason of its treatment so that thecontained bacteria cannot grow. They

remain dormant in the milk, but assoon as it is diluted to a normalconsistency, growth takes place, andthe milk rapidly spoils. Condensedmilk is prepared by adding cane sugarto fresh sweet milk, then evaporatingthe mixture to one-third the originalvolume, forming a semi-solid product.Syrups owe their keeping qualities tothe same factor, as condensed milk,i.e., the high consistency.

Milk is also preserved by whollyevaporating the water, thus leaving adry powder, which on being mixed withwater again will have much the sameproperties as the original milk. Variousmethods have been devised for thepreparation of these milk powders, all

of which have been patented by theinventors. If the powder is to be keptfor long periods, skim milk must beused, since the fat slowly undergoeschanges which cause it to have a rancidodor. These dry preparations arelargely used by bakers in place of freshmilk.

CHAPTER VII.

BACTERIA AND BUTTERMAKING.

In the making of butter it is necessaryto concentrate the milk fat into a smallvolume. This process, known ascreaming, may be accomplished bygravity, if the milk is allowed to standundisturbed, the fat globules risingslowly to the surface. Much more rapidseparation may be secured, by placingthe milk in a rapidly revolvingcontainer in which it is subjected to

centrifugal force, which causes theheavier parts of the milk to pass to theoutside of the bowl, while the lighterpart, the fat, collects at the center ofthe revolving bowl. There is anenormous number of fat globules inmilk, over 5,000,000,000 in each cubiccentimeter, and as these move throughthe milk serum, they carry with themmany of the bacteria. The cream is thusmuch richer in bacteria than is the skimmilk, or even the milk beforeseparation. Besides the mechanicalseparation in the manner described, themethod of creaming is of importance,in determining not only the number butalso the kind of bacteria in the cream.

Methods of creaming. In the shallow-

pan method of creaming, the milk iskept at ordinary room temperatures.These temperatures favor especiallythe growth of the acid-formingbacteria. The milk is usually sour bythe time the cream is removed from it;consequently, the bacterial content ofthe cream is high. Moreover, the creamis exposed to air contamination, and isthus seeded with molds, and thoseforms of bacteria that are always foundin the air. The cream obtained in thismanner is likely to contain not onlynumerous bacteria, but a great varietyof forms, some of which undoubtedlyare the cause of the poor keepingqualities of butter made from suchcream.

In the more modern method of gravitycreaming, in which the milk is placedin deep narrow cans kept in cold water,the conditions are not favorable for thegrowth of acid-forming bacteria. If themilk is produced under cleanconditions, and is placed in cold waterat once, the bacterial content of thecream will be low, and it will be lesslikely to contain undesirable formsthan the cream which is obtained fromthe shallow pans.

In separator cream the bacteria will berepresented by the kinds present in themilk at time of separation. If this milkis quite old, the cream will containlarge numbers of bacteria; if, however,early separation is made and the milk

is clean, the bacterial content of thecream will be low.

Types of butter. Butter may be dividedinto two types—acid or sour-cream,and sweet-cream, depending uponwhether the cream is allowed toundergo the acid fermentation or notbefore it is churned. In southernEurope, it is the custom to churn thecream as sweet as possible, and theresulting product possesses only thenatural, or primary milk flavor. To oneaccustomed to butter made from souror ripened cream, this taste is flat, andif the butter is free from salt, mayremind one of grease. Sweet-creambutter has a delicate flavor when it ismade from good milk, and the taste for

it is rapidly acquired. In some centers,as in Paris, the market demands thistype of butter quite exclusively.

If the cream is allowed to undergo theacid fermentation before churning, thebutter has a much higher degree offlavor and one that differs materially inkind. Under primitive methods, it wasdifficult to keep the cream sweet untilit could be churned. On the small farmwith gravity creaming in shallowvessels and infrequent churning, thecream was certain to be sour whenchurned. Undoubtedly, the making ofbutter from sour cream came into usebecause of its greater convenience;people became accustomed to sour-cream butter, and at the present time it

is used in the greater part of the world,and is the type made in all of the greatdairy countries.

Ripening of cream. In modern dairypractice the souring of the cream iscalled the ripening process, and is,where the best methods are employed,largely under the control of the buttermaker. The changes that go on in theripening process are the same as havebeen discussed in the acid fermentationof milk. The increase in acid isaccompanied by an enormous increasein the number of bacteria; the ripecream will contain hundreds ofmillions of bacteria in each cubiccentimeter. The effect of this germ lifeis to improve or injure the butter,

depending upon the class of bacteria towhich it belongs. The problem of themodern butter maker is to control thekinds of bacteria growing in the cream.

The temperature at which cream is heldduring the ripening process is favorableto the growth of the acid-formingbacteria; hence, in ripe cream, they arepractically the only kind of bacteria tobe found. It must be rememberedhowever, that there are differentclasses of acid-forming organisms,some of which produce desirableflavors, while others are distinctlyharmful.

The intensity of flavor of butter is, in ageneral way, directly related to the

amount of acid that is formed in thecream. A low acidity at time ofchurning is usually associated with amild flavor, while a higher degree ofacidity, up to a certain point, imparts amore pronounced flavor to the product.If cream is over-ripened, the quality ofthe flavor is seriously impaired.

In determining the acidity of cream, adefinite volume is taken, and theacidity determined by titration,expressing the results as such a percent of lactic acid. Manifestly, theamount of fat in the cream influencesthe apparent per cent of acidity. Theacidity will not usually exceed 0.5 to0.7 per cent, but in reality the serumwill contain more than this, as the acid

is formed in the serum, the butter fathaving no role whatever. In a very richcream, 40 to 50 per cent fat, it isimpossible to develop more than 0.4 to0.5 per cent of acidity, and the flavor ofthe butter will be low, because of therelation between the amount of acidand fat, while in a thin cream havingthe same acidity, the ratio between theamounts of fat and acid will be verydifferent. For example, in one hundredpounds of 50 per cent cream of 0.5 percent acidity there will be one-halfpound of acid and fifty pounds of fat;in the same quantity of creamcontaining 20 per cent of fat andhaving an acidity of 0.5 per cent therewill be one-half pound of acid to

twenty pounds of fat. The flavor of thebutter from the rich cream will be quitedifferent in intensity from that madefrom the thinner cream.

The acidity of cream cannot bedetermined with any degree ofaccuracy by the taste or odor. Everybutter maker should have some methodof determining the degree of acidity inhis cream, so that he may better controlthe flavor of his product. Severalmethods have been devised for thispurpose and the necessary apparatus issold by all dairy supply houses.

The effect of the ripening of the creamis shown not only in the flavor of theproduct, but in a number of other ways.

Sour cream churns more easily, andmore exhaustively than does sweetcream. It is supposed that the fatglobules are surrounded by a film ofalbuminous material which preventstheir coalescing readily. During theripening process, the action of the acidapparently dissolves this envelopingsubstance, and the globules coheremore easily in the churning process.

When raw cream is used the ripened-cream butter keeps better than thatmade from sweet cream. In sweetcream there are few lactic bacteria, themajority of the bacteria present beingof various kinds, many of which maybe injurious, so far as the keepingquality is concerned. In sour-cream

butter the lactic bacteria make up over99 per cent of the bacteria present, andtheir presence tends to prevent thedevelopment of undesirable non-acidforms.

Source of butter flavor. The flavor ofripened-cream butter has been shownto be directly connected with the acid-fermentation of the cream. The amountof lactic acid formed from the sugarfermented is dependent upon the kindof bacteria present. The acid-producingorganisms that are desirable from thestandpoint of the butter maker formcomparatively small amounts of otherby-products, but these undoubtedlyaffect the flavor of the butter. As fatshave the power of absorbing odors, the

butter fat absorbs some of the by-products of the acid fermentation, thusacquiring a certain aroma and flavor.

It is not necessary that the cream beripened, in order to have the fat acquirea flavor, for if sweet cream is churnedwith a considerable proportion of sourmilk, the butter will have much thesame flavor, both as to intensity andkind, as though the cream had beenallowed to sour naturally. A process ofbutter making known as the LeClairmethod is based on this principle. Theflavor-producing substances can alsobe absorbed by the butter after it ischurned, by working the butter incontact with sour milk. Attempts havebeen made to add pure lactic acid to the

cream, instead of allowing the acid tobe formed by the bacteria, but whilethe physical effect on the cream is thesame, the flavor and aroma of thebutter are deficient, because the aciditself does not supply the necessaryaromatic products. This emphasizes theimportance of the by-products of theacid fermentation other than the lactic-acid.

In the past numerous attempts havebeen made to find organisms thatmight be added to the cream, in orderto produce the delicate flavorcharacteristic of the best type of butter.Some bacteriologists have claimed thatthe source of the flavor-givingsubstance was to be found in the

decomposition products of thenitrogenous constituents of the milk.None of these attempts have stood thetest of practical use in creameries, andit has been demonstrated that the finesttype of butter can be made by the useof lactic bacteria alone. Formerly,when butter was made wholly fromcream soured under natural conditions,a much higher degree of flavor wasdeveloped. Under present marketdemands, a less pronounced flavor isdesired, a condition more readily metby the use of modern methods.

Importance of butter flavor. Theimportance of flavor in determining thecommercial value of butter isevidenced by the relatively high value

placed upon this factor in scoring, viz.,flavor, 45 points; body or texture, 25points; color 15; salt 10; and package 5points. The factors on which butter isjudged, are with the exception offlavor, wholly under the control of themaker, but as the production of flavoris dependent on the kind of bacteriapresent in the cream, it is a far moredifficult matter to control, and yet it isof the utmost importance indetermining the value of the product.

The flavor of the butter is dependent onthe quality of the cream. If this is dirtyand sour, the maker has little controlover the type of fermentation, andhence, little control of the flavor of thebutter. This has led in some cases to

the grading of the cream, basing thedivision on the acidity, flavor, and fatcontent. Such practice is entirelyjustifiable, as a better quality of buttercan be made from fresh, sweet creamthan from that already fermented. It isnoteworthy that the quality of butterhas not improved since the introductionof the centralizer system, in whichcream is shipped for long distances.

Control of the type of fermentation.In the older methods of butter making,there was little or no control of the typeof fermentation that took place in thecream. Where milk is produced underclean conditions, and kept at ordinarytemperatures, it will generally undergofermentation changes, due to the

desirable type of acid-formingorganisms. In milk, which is lesscarefully handled, the undesirablebacteria are more abundant and thequality of the butter of lower grade.When butter was made on the farm,before the development of the factorysystem, it was not a question of vitalimportance whether the product wasuniform from day to day, but with theadvent of the modern creamery, turningout thousands of pounds of butter perday, and with the extension of themarkets for the product, the question ofuniformity came to be of muchimportance. A uniform product can besecured only by the control of the typeof fermentation in the cream, or by the

control of the kinds of bacteria thatcause the souring of the cream. Modernmethods of butter making have beendevised on the basis of an improvementin the ripening process.

Starters. From the earliest practice ofallowing the cream to stand untilsufficient quantity had accumulated forchurning, it was only a step, but a mostimportant one, to the addition of sourmilk, sour cream, or butter milk, tohasten the ripening process. This wasthe beginning of the modern starter.Experience demonstrated that theaddition of these already fermentedliquids exercised a desirable effectupon the production of butter flavor,even though, at that time, the

phenomenon of milk fermentation wasnot satisfactorily understood, and therelation of bacterial by-products to theproduction of flavor in butter was notrecognized.

As a result of experience alone,improvements in the development ofthe "home made" starter took place. Bycareful selection of clean milk, and thenatural fermentation of this undercarefully controlled conditions, as wellas the control of the temperature of thecream during the ripening,improvement in the technique of creamripening gradually developed. Moreand more attention was given to thepreparation of the starter, and itspropagation from day to day, under

conditions which would prevent itsdeterioration. This method of utilizingnaturally fermented milk or cream wasgradually extended, until it becamealmost universal in the larger butter-producing districts.

In 1890 a more refined and scientificprocess was introduced by the Danishbacteriologist, Storch. Recognizing thefact that butter flavor was attributableto the development of the bacteriapresent in the ripening cream, heconceived the idea of isolating thevarious types of organisms found inmilk and testing them as to their effecton the quality of flavor. Selection wasthen made of the most favorableflavor-producing types, and these were

propagated in suitable culture media,such as skim milk, which was renderedmore or less perfectly sterile bypasteurization or sterilization. Undersuch conditions the addition of aselected ferment could be made to thefresh cream, and so control the type offermentation which occurred therein.An essential requisite in any organismused for this purpose must be theability to produce relatively largeamounts of acid rapidly at ordinaryripening temperatures, and also to formsufficient quantities of the properflavor-producing substances to imparta suitable flavor to the butter fat. Suchstarters are known as pure culture orcommercial starters, and are prepared

in both liquid and dry form. At presentthey are used to a greater or less extentin all of the leading dairy districts.

Liquid starters consist of a mass ofsterile nutrient medium, milk or beefbroth, inoculated with the pure culture.The dry starters are made by addingliquid cultures, containing the growingbacteria, to some absorbing material,such as milk sugar, milk powder, orstarch, the whole mass being dried atlow temperatures, so as not to injurethe bacteria. Under such conditions thebacteria, exist in a dormant state, andare protected from their own by-products, to which they would beexposed if maintained in liquidcultures. The keeping quality,

therefore, of dry cultures, is muchbetter than that of liquid cultures.

By the use of the pure-culture starters,the butter maker is able to add to hiscream the same kind of bacteria fromday to day, and the butter will be moreuniform than when the less constanthome-made starter is employed. Incream to which the starter is added,there are present a greater or lessnumber of acid-forming bacteria,depending upon the age of the cream,and upon the condition under which itwas produced. These will grow duringthe ripening process, and the flavor ofthe product will be the result of themixture of the bacteria in the cream.The maker can not, therefore, be

certain that the addition of a pureculture to raw cream will effectivelycontrol the type of fermentation. Thiscan be secured only by first destroyingthe existing bacteria in the cream,before the selected culture is added.Heating the cream accomplishes this;and in cream thus freed from thevarious kinds of bacteria, the buttermaker can insure the dominance of thedesirable types, contained in the pure-culture starter. If the cream can beobtained in a sweet condition, themaker through this process ofpasteurization, and the use of purecultures, secures almost perfect controlover the type of fermentation thatoccurs in the cream, and thus exercises

control over the degree and kind offlavor of the product. This mostscientific type of butter making is nowused by the most progressive buttermakers in the leading butter-producingregions of the world.

Pasteurization of the cream alsodistinctly improves the keeping qualityof butter, a condition doubtless due tothe freedom of the same fromorganisms other than the lacticbacteria. This is a factor of as muchimportance as uniformity, becauseunder modern business conditions, thesurplus production must be kept instorage, and it is essential that thequality should not deterioratematerially during this time.

Process of pasteurization for buttermaking. In the pasteurization ofmarket milk, it is necessary to take intoaccount the effect of heating on thephysical and chemical properties of themilk, and the degree of heat that can beemployed is limited. In pasteurizingcream for butter, there is no suchlimitation, and the cream may beheated to any temperature desired. InDenmark where the process ofpasteurization has been used mostextensively, temperatures ranging from176° F. to 190° F. are used. Themachines are of the "continuous flow"type, and the cream rather than thewhole milk is treated. To prevent thespread of tuberculosis and other

diseases, the Danish governmentrequires that all cream and milk beheated to 176° F., before the skim milkor butter milk is returned to the farms.

The heating of the butter fat to hightemperatures has an injurious effect onthe texture of the butter, unless thecream is cooled to 50° F., for a periodof at least two hours previous tochurning.

Propagation of starters. As has beenpreviously shown, the quality of butterdepends on the kind of bacteria in thecream or in the starter added. Thecommercial starters contain lactic acidbacteria that have been selected withespecial care; most of the starters now

sold contain but a single kind ofbacteria; hence, are often called pure-culture starters. The package purchasedcontains but a small quantity, andbefore the starter can be used in theripening of cream, it must be increasedin amount. It must also be propagatedfrom day to day so that a fresh startershall be available daily for addition tothe cream. The propagation of thestarter must be done with especialreference to keeping it in goodcondition and in as high a state ofpurity as possible.

In the past the starter was propagated,by adding the contents of the bottlepurchased to a small amount of milkthat had been heated and cooled; this, if

kept in a warm place, would be curdledin twenty-four hours, and could be usedfor the inoculation of a large mass ofmilk, that had been treated in a likemanner, and which, when curdled, wasadded to the cream; a small amountwas saved for the purpose of againinoculating a mass of milk that hadbeen heated and cooled. Following thismethod it was very difficult to keep theculture from becoming contaminatedwith other forms of bacteria. Morerecently the most successful buttermakers have propagated the so-called"mother starters" in small vessels, andhave used the larger mass of starter forthe inoculation of the cream alone.

Glass vessels are preferable for the

propagation of the mother starterssince they are impervious and throughthe transparent wall the condition ofthe ripened starter can be more easilydetermined than in a metal orearthenware vessel. An ordinary milkbottle with an inverted tumbler for acover, to protect the starter fromcontamination from the air, is a mostconvenient vessel.

The starters may be propagated eitherin whole or skim milk; the former ispreferable since, in most creameries, itcan be more easily selected. Thequality of the milk used has much to dowith the quality of the starter; it shouldbe as fresh and clean as it is possible toobtain. The clean bottle should be

filled half to two-thirds full, coveredand heated in some manner so that themilk shall be at a temperature close tothe boiling point for fifteen to twentyminutes. The heating may be done byplacing the bottles in water, which isheated on a stove or by steam, or thebottles may be subjected to streamingsteam. The milk is cooled quickly andthe contents of the package purchasedadded and well mixed with the milk. Inthe case of the dry starters, the mixingshould be done with especial care. Thebottle is kept in a warm place and intwenty-four to thirty-six hours, themilk should be curdled. A secondbottle must be treated as before andinoculated from the first, and the

process repeated daily since thebacteria must have fresh food, if theyare to be maintained in good condition.

In order to accomplish this, the makermust be able to maintain constantconditions from day to day, especiallywith reference to the amount of theripened starter that is transferred to thefresh bottle of milk, and thetemperature at which the bottles arekept. A spoon, arranged as shown inFig. 31, enables one to carry a definiteamount of the ripened starter to thebottle of milk to be inoculated and aconstant temperature box (Fig. 32)permits of the maintenance of the sametemperature from day to day. Throughcareful supervision of these points, and

by taking care at every step to avoidthe introduction of contaminatingorganisms, the purity of the culture canbe maintained, and the bacteria kept ina healthy condition.

The starter is used because of the acid-forming bacteria it contains; it is saidto be ripe and in the best condition foruse at the time it contains the greatestnumber of living bacteria. It has beenfound by experiment that this is at thetime the milk curdles at ordinarytemperature, or when the acidity isabout 0.6-0.7 per cent. If the acidity isallowed to increase to 0.8 or 0.9 percent, the number of bacteria will beless and a larger amount of the startermust be used in order to ripen a

definite amount of cream in the desiredtime. The use of an overripe startermay also have an injurious effect onthe flavor.

FIG. 31.—BOTTLE FOR MOTHER STARTERS.

A milk bottle with a tumbler for acover and a spoon for inoculating the

other bottles enables the buttermaker to propagate the starters

without contamination.

The ripened starter should be perfectlyhomogeneous, showing no bubbles ofgas or free whey; the odor should beagreeable and the acid taste mild; onshaking, the curd should break up intoa smooth, creamy liquid free fromlumps. This is especially important inthe starter that is to be added to thecream, since otherwise the startercannot be uniformly mixed with it andwhite specks of curdled casein will benoted in the butter.

FIG. 32.—AN INCUBATING CHAMBER FOR

STARTERS.The inner compartment will hold apail of water and the bottles for themother starters. The temperaturecan be kept at any desired point bythe use of warm or cold water. Thefour-inch space between the walls is

filled with hay or mineral wool.

The firmness of the curd is not sodependent on the amount of acidformed as upon other factors. If thecurd shrinks to any extent and the wheyis expressed, it is certain to produce astarter that will contain lumps thatcannot be broken up. With a pureculture of lactic bacteria, there is littledifficulty in this regard, but as soon asgas-forming bacteria are introduced,

trouble is likely to result.

In the propagation of starters, it isalways to be remembered that thebacteria, although invisible to the eye,are living things, and unless conditionsare favorable in every particular, it isimpossible to keep them in a healthycondition, so that growth in the creamis rapid, producing the acid demandedfor churning, and imparting to thebutter the desired flavor, both as todegree and kind. No part of the dailyroutine of the butter maker should beperformed with more care than thepreparation of the starters, both themother starters, and the larger one foraddition to the cream. The latter canbest be made in one of the many forms

of starter cans now on the market, sinceby their use, the maker can heat andcool the milk with little trouble, andcan maintain the starter at any desiredtemperature. Better starters cannot bemade in them than by the use of simpleand improvised apparatus, but betterresults can be obtained with the sameexpenditure of time and labor.

In the handling of the large starter, careshould be used not to overripen, sincethe larger quantity is more likely to"whey off" than is the smaller starter.Skim milk rather than whole should beused for this. It should be selected withcare and heated to 200° F. for thirtyminutes. When it is impossible tosecure fresh milk for starter making

purposes, either condensed skim milkor milk powder may be used. Thecondensed milk is diluted with wateruntil its volume is about the same asthe milk before concentration; themixture is then treated the same asfresh milk, being heated and cooledbefore inoculation. In the case of milkpowder, one part of the powder isadded to ten or twelve parts of water,allowed to dissolve as far as possible,and the mixture heated and cooled.Either of these liquids will givesatisfactory starters; the cost howeveris high, and in most places milk can beobtained more cheaply. The inoculationand the temperature should be socontrolled, as to ripen the starter at the

time it is to be needed. Theseconditions must be determined by themaker for himself. It should beremembered that the bacteria growmuch more rapidly, as the temperatureis increased; and hence, the amount ofinoculation is dependent on thetemperature at which the starter is to bekept.

When the starter is propagated underpractical conditions, it sooner or laterdeteriorates, either in acid production,or in flavor, and a new pure culturemust be procured from themanufacturer. It is impossible to give ahard and fast rule as to the length oftime a starter can be kept in goodcondition. It will depend on how well

the maker satisfies the conditionsnecessary for maintaining its purityand strength. The use of imperfectlysterilized milk, or dirty utensils sooncontaminates it; overripening is likelyto injure the flavor. One of the mostfrequent troubles encountered is theappearance of a slimy or ropycondition in the starter, although theacidity developed may be normal andthe flavor desirable. It has been foundthat this condition is not necessarilydue to contamination, as wasconsidered true in the past, but ratherto some change in the lactic bacteriathemselves. If the propagation iscontinued, the slimy condition willoften disappear.

Starters in "process" butter andoleomargarine. The advance whichhas recently been made in the scienceand practice of cream ripening andbutter production is utilized mosteffectively in the treatment of cream inthe renovating process. Old, soured,and stale cream is reduced in acidity bythe addition of lime. The cream is thenpasteurized and aerated to expel theodors as much as possible. A largeamount of starter is then added and thecream immediately churned. Underthese conditions, the bad flavors arematerially reduced in intensity, anddesirable flavors absorbed by the fatfrom the selected starter used. It is thuspossible to produce butter of good

quality from cream that would at firstbe regarded as quite unsuitable forbutter production.

In the manufacture of oleomargarinethe same principle is utilized. Thebutter aroma and flavor is imparted tothe neutral oils and tasteless fats bymixing the same with a properlyprepared starter. Renovated or processbutter is given a desirable flavor in thesame way.

Wash water. It has been found that thepurity of the water used in washing thegranular butter has a marked influenceon the keeping quality. If the water isfrom a shallow well into which surfacewater finds its way, it is certain to

contain large numbers of those types ofbacteria that are found in the soil,while if it comes from a deep well thatis properly protected from surfacecontamination, the bacterial content ofthe water will be low and no injuriouseffect on the butter will be noted.When it is impossible to obtain purewater for washing purposes, a propersupply may be secured by sterilizingthe water. The most convenient way ofheating the water is by the directinjection of steam. It is necessary touse that coming directly from theboilers and not the exhaust from theengine, since the latter is likely tocontain small amounts of oil that willimpart to the butter an objectionable

flavor. After cooling, the water is readyfor use. It has been shown that the costof treating an impure water is morethan covered by the increased returnsfrom the product.

A pure and healthful water supplyshould be one of the essential things ofevery dairy, creamery, and cheesefactory, not only for the sake of thequality of the product, but also to avoidcontamination of products withdisease-producing bacteria.

Bacteria in butter. The germ contentof butter will depend on the type ofcream. Sweet-cream butter contains butfew bacteria. In sour-cream butter thecontent in bacteria will be greatly

increased, especially as to lacticorganisms. Often, it may amount toseveral millions of organisms pergram. The germ content of butter issaid to be greater on the outside of apackage than within the mass, duedoubtless to the free access of air, thusfavoring the growth of the aerobicforms.

The composition of normal butter doesnot favor the growth of the majority ofkinds of bacteria that are contained init. The washing process removes muchof the material suitable as food for thebacteria, such as sugar and albumen. Ifconsiderable butter milk is left in thebutter, the growth of bacteria will bequite rapid, at first, but does not

continue for any considerable length oftime. The addition of salt also tends torestrain the growth of most kinds ofbacteria.

Butter is at its best when it is perfectlyfresh. Deterioration begins within ashort time and the rapidity with whichthe changes go on is dependent on thetemperature at which the butter isstored. The temperature of the butterrooms in the large cold storage plantsis kept below 0° F. The butter in suchrooms will deteriorate very slowly, buton removal from the cold rooms and instorage at ordinary temperaturesdeterioration goes on more rapidly thanwould have been the case when thebutter was fresh. At the temperature of

an ordinary refrigerator the changes goon much more rapidly. This fact hasoften been looked on as indicating thatthe factors causing the changes arebiological ones. The influence oftemperature in accelerating the changeswould be the same if no biologicalfactor were active.

That biological factors are ofimportance is indicated by the fact thatthe keeping quality of the product isprofoundly affected by the quality ofthe cream. Butter made from sweet,fresh cream, that has been thoroughlypasteurized, has the best keepingquality, while butter made from suchcream, but not pasteurized, has thepoorest keeping quality, especially

when no salt is added. Every process bywhich the desirable lactic bacteria areincreased in proportion to other kindshas a marked effect in enhancing thekeeping quality of the butter. Thus, theuse of pure cultures in raw cream, andpasteurization together with the purecultures, have a marked beneficialeffect.

The addition of preservatives exerts aneffect on keeping quality. Borax is thechemical most frequently employed forthis purpose. Its use is allowed inAustralia and New Zealand in butterthat is shipped to England, but the useof all preservatives is forbidden in theUnited States.

The size of the package also has aneffect on the keeping quality; thesmaller the package, the greater is thesurface exposed to the air and the morerapidly the butter deteriorates. Butterused in the United States Navy ispacked in hermetically sealed cans soas to exclude the air as far as possible.

From the fact that any condition whichrestrains or inhibits the growth ofmicro-organisms has a tendency toimprove the keeping quality of butter,it would appear that the detrimentalchanges in the quality of butter are dueto biological causes. The most commondefect known is that usually referred toas rancidity. There are, however,different types of changes that are

probably included under this head andit is very probable that different causesare operative in their production. Truerancidity is probably due to biologicalcauses; the so-called tallowy change, inwhich the butter acquires the odor oftallow is probably due to the combinedaction of light and air on the fat.

Bacterial defects in butter. There area number of defects in butter that arepositively known to be due to thegrowth of bacteria in the milk orcream, or in the butter itself. The lackof flavor is looked upon as a defect inthe case of ripened-cream butter. Itmay be due to insufficient ripening ofthe cream, or to the lack of acid-forming bacteria that produce the

desirable flavor-forming compounds.Not all acid-forming bacteria are ableto produce favorable, flavor-givingcompounds; hence, sour cream buttermay sometimes be deficient in flavorby reason of this fact.

Putrid butter. This specific buttertrouble has been observed in Denmark,where it was first studied by Jensen.Butter affected by it rapidly acquires apeculiar putrid odor that ruins it fortable use. Sometimes this flavor maybe developed in the cream previous tochurning. It may be caused by anumber of bacteria.

Turnip flavored butter. Buttersometimes acquires a flavor

resembling turnips. This trouble maybe due to the feeding of such roots, thearomatic substances peculiar to thembeing absorbed directly by the milk andthus transferred to the butter.Weigmann traced a similar flavor tocertain bacteria that entered the milkfrom barn filth.

Cowy odor in butter. There issometimes to be noted an odor in butteras in milk that resembles that of thecow stable. Usually this defect hasbeen ascribed to the absorption of theseodors directly by the milk. Organismshave also been described that impart tothe butter a very similar odor. Bitterbutter may be due to the feed that isconsumed by the cow, or it may be due

to those forms of bacteria that producea bitter fermentation of the milk.

Other abnormal flavors. Among thenumerous abnormal flavors that havebeen noted in butter is one of quitefrequent appearance, the so called"fishy" flavor. It is now believed bymany that this flavor is due to thepresence of small amounts of iron orcopper salts that have been introducedinto the milk from utensils from whichthe protective coating of tin has beenworn. If the milk or cream stored insuch utensils develops any markeddegree of acidity, the acid will dissolvea small amount of the iron or copper.The fishy flavor has not been found insweet-cream butter as would be

expected from the above explanation.In fresh butter a metallic taste issometimes present. It is believed bysome that on storage this flavorchanges to the fishy flavor.

All utensils used for the storage ofmilk and cream should be kept in goodcondition so as to prevent the acid milkor cream from coming in contact withiron or copper.

FIG. 33.—MOLDY BUTTER.The mold grows on the paper in

which the butter is wrapped ratherthan on the butter. The print on theleft was wrapped in the same paperas the print on the right except that

the parchment cover had beensteamed for a few moments.

Moldy butter. A defect that causes agreat amount of loss is thedevelopment of mold on the surface ofthe butter, either in tubs or in prints.This trouble is easily prevented. Butteris not well suited to the growth ofmold, but the paper used for lining thetubs, or wrapping the prints is anexcellent medium for mold growth.The wood of the tub also furnishesample food for this type of life,especially where the wood contains any

sap. One other essential condition formold growth is a supply of oxygen. Themold spores are widely disseminated,and are always to be found on thebutter tubs and on the paper. Thenumber is not likely to be sufficient tocause trouble unless the tubs and paperhave been kept under such conditions,as to allow growth to take place onthem before use. During damp, hotweather, the amount of moistureabsorbed by these materials is oftensufficient to allow molds to grow onthem. This trouble can be prevented bythe storage of tubs and paper in a cleandry place, or by a disinfectingtreatment which will destroy the moldspores. The most successful method of

treatment of tubs is to apply paraffin tothe inner surface, which can be easilydone by the use of some one of thevarious machines now on the market.The thin layer of paraffin excludes themoisture from the wood, and alsoprevents the mold from obtaining asupply of oxygen for its growth. Thetubs may be steamed, treated with hotwater, or filled with a dilute solution offormaldehyde, and allowed to standovernight. Soaking in brine as isusually done in the creameries is ofsome effect, but will not completelykill mold spores.

FIG. 34.—MOLDY BUTTER.The butter was placed in a paraffinedtub, but the paper was not treated so

as to destroy the mold sporesthereon.

Butter may mold where the tubs havebeen thoroughly treated, because of themold spores on the paper used for thelining. One of the black molds is ableto thrive on parchment paper wheneverthe air is damp. In the past but littleattention has been paid to the paper asa source of trouble. It is certain that itis often at fault, and that as muchattention should be paid to the paper asto the tub. A most efficient way oftreating paper, either for tub liners orprint wrappers is to place same in

boiling water for a few minutes.

CHAPTER VIII.

BACTERIA AND CHEESEMAKING.

Butter, such as that of the sweet-creamtype that is highly esteemed in manyparts of the world, may be madewithout the aid of bacteria, but noimportant kind of cheese can be madeunder commercial conditions withoutthem.

Types of cheese. Cheese consists of thefat and the precipitated casein of milk,together with a large amount of water

and the salts found in milk. Thenumerous types of cheese may bedivided into two groups, depending onthe manner in which the curdling of themilk is brought about. Sour-milkcheese is made from curd, formed as aresult of the acid fermentation of themilk. Thus, at the very first stage in themaking of this type, the importance ofbacteria is apparent.

The second type is that made fromcurd, which is precipitated by theaddition of rennet to the milk. Thistype may also be divided into twogroups, depending upon their texture;the hard cheese, and the soft cheese.The ordinary cheddar, the commonAmerican type, is the most important

example of the hard cheese;Limburger, of the soft cheese. Cheeseare designated as hard or soft,depending upon the amount of wheythat is retained in them during themaking process. The moisture contenthas an important influence on the typeand amount of life that develops on andin the curd mass, and as will be seen,the ripening and flavor of the cheeseare dependent upon these biologicalfactors.

The two groups of hard and soft cheesehave no sharply defined limits, butmerge into each other. The extremetypes of the hard cheese are so dry andfirm that they can be cut only withdifficulty. Such cheese are used

primarily as condiments to impart aflavor to certain dishes, as macaroni,and for this purpose are grated. Theextreme type of soft cheese is a soft,pasty mass and can be easily spreadwith a knife.

Hard cheese, because the ripeningprocess goes on uniformly throughoutthe entire mass of cheese, may be madeof any size which permits ofcommercial handling. They can also bekept for long periods and preserve theirgood qualities. Soft cheese are made insmall sizes, since on account of theirconsistency, they could not otherwisebe handled, and also because of themanner of ripening. The ripening is dueto the action of organisms developing

on the surface, the by-products ofwhich diffuse into the curd. If thecheese are too large, the outer layersbecome overripe, while the interiorremains more or less unchanged, orinsufficiently changed. Soft cheesemature much more rapidly than hardcheese; consequently they are shortlived.

Although made from the samesubstance, milk, it is noteworthy thatthere are over four hundred varieties ofcheese produced. Most of these findonly a local market where made. Lessthan a dozen varieties are to beregarded as general articles ofcommerce.

Quality of milk. In the making ofbutter there are a number of processesthat the maker can use when he findshimself obliged to utilize poor milk.The milk can be pasteurized and theharmful bacteria thus destroyed;desirable kinds can then be added inthe form of a pure-culture starter.Pasteurization also drives off some ofthe volatile by-products of the firstacid fermentation. By the use of thesemeans, the maker can prepare a verygood product from poor material.

In the making of most kinds of cheese,especially those of the greatestcommercial importance, the cheesemaker can call to his help no such aids,but must use the milk as it is brought to

him. It is possible to prepare certainkinds of soft cheese from pasteurizedmilk that differ in no essential pointfrom the same cheese made from rawmilk. Hard cheese are also made frompasteurized milk, but in most casessuch cheese differ, especially in thedegree of flavor, from that made fromunheated milk. It is quite probable that,as the factors concerned in the ripeningof cheese become better known,methods will be evolved for thesuccessful production of many kinds ofcheese from pasteurized milk.

It has been shown that the quality ofmilk is almost wholly dependent uponthe number and kinds of bacteria itcontains. These bacteria pass into the

cheese, and there produce the sameproducts as they would have done inthe milk itself. In butter making,practically all processes are under thecontrol of the maker, until the productis ready for the market; but cheese, onthe other hand, passes through acomplicated series of changes after ithas left the maker's control. During themanipulation of the milk and the curdin the vat, he can exert some influenceon the quality of the product, but he ismuch more dependent on the quality ofthe milk than is the case in buttermaking.

Every effort should therefore be madeto furnish to the cheese maker thequality of milk from which he can

prepare fine cheese. In other words, themilk should be produced under cleanconditions and carefully cooled andhandled until delivered to the maker.Poor milk from a single farm may havesuch an effect upon the cheese madefrom the milk of twenty farms as todepreciate the selling value of theentire product several cents per pound.

The tests that have been previouslydescribed (p. 105) have been devisedespecially for testing the quality of themilk for cheese making purposes, andare of the greatest service to the makerin tracing the source of poor milk.

Cheddar cheese. The first step in themaking of cheddar cheese is the

"ripening" of the milk, or thedevelopment of a small amount of acid.In this fermentation, the developmentof acid is preceded by an enormousincrease in the number of acid-formingbacteria. Milk for cheese makingshould show an acidity of about 0.2 percent or slightly more than in freshmilk. In other words, the maker wishesthe milk to be in such condition,bacteriologically, that if kept at atemperature favorable for the growth ofthe acid-forming bacteria, the aciditywill increase rapidly.

The curdling of the milk to precipitatethe cheese solids is produced by theaddition of rennet, which is obtained byextracting the fourth stomach of the

young calf with a solution of commonsalt. In the past the maker prepared hisown rennet solution from the driedstomachs ("rennets"), but at present,the extract is prepared commercially,in a much more uniform manner. Therapidity of the curdling is dependentupon the acidity of the milk. In order tosecure proper rennet action, a slightincrease of acid over that found infresh milk is usually necessary; thus atthe very beginning of the process ofmaking cheddar cheese, the bacteriaare of importance.

As the milk curdles, the bacteria areenclosed in the curd as are the fatglobules. The curd is cut into smallfragments by means of a curd knife,

and as the mass is warmed, the aciddevelops, causing the curd particles toshrink, thus expressing the whey.Within a short time, the volume of thecurd is not more than one-eighth that ofthe milk, but in the curd are held over75 per cent of the bacteria of the milk.To secure rapid curdling in the vat, themilk is warmed to 85° to 90° F., atemperature that is most favorable forthe growth of the lactic bacteria. Sincethere is a large number of bacteriaconcentrated in a small volume, andthe temperature, as well as all otherconditions, is favorable to growth,multiplication of the bacteria goes onrapidly, and as a consequence, acid isformed in large amounts, as is shown

by the following figures given byPublow for the manufacture of theexport type of cheddar cheese:

Acidityof milkbeforeaddingrennet

.2to.21

percent

Acidityof wheybeforeheatingcurd

.14to.145

"

Acidityof wheybeforeremoving

.16to "

fromcurd

.18

Acidityof wheycomingfrom thecurdafterremovalof wheyand curdis packed

.24to.30

"

Acidityof wheycomingfromcurd

.65to.75

"

beforemilling

Acidityof wheycomingfromcurdbeforesalting

.90to1.10

"

If the milk had been kept at the sametemperature as the curd, the aciditywould have increased much moreslowly since the acid would have beendistributed through a larger volume. Inthe cheese curd the same amount ofacid is probably formed, as would havebeen produced in the total amount of

milk during the same interval.

The acid produced by this bacterialactivity has a most marked effect onthe curd. At first the curd masses aretough and firm, the particles showingno tendency to adhere to each other. Asthe acid increases in amount, the curdbecomes plastic, the outer surface ofthe particles adhering or "matting," asthe maker expresses it. The result is asolid coalescent mass of curd, which iscut into small pieces, i.e., "milled,"before it is put to press. The acidallows the blending of the pieces underthe influence of the pressure so that acheese is one single mass. Undercertain abnormal conditions, thedevelopment of acid may be interfered

with and the particles of curd fail tomat, in which case, the cheese will becrumbly when it is cut. Thedetermination of the proper time forpressing is made by the application ofwhat is known as the hot iron test. Thisis made by determining the length ofthe "strings" or "threads" which can bedrawn from a mass of curd when it isbrought in contact with a hot iron at acherry red heat, the length of the curdthreads being a measure of the amountof acid that has been formed in thecurd.

The rate of acid formation within thecurd particles is also measured bydetermining the acidity of the whey asit comes from the curd at different

stages in the making. This test, whichis often used in place of the "hot iron"test is carried out in the same manner,as in determining the acidity of milk orcream. The quality of the cheese, bothas to texture and flavor, is dependent toa great degree upon the amount of acidthat is formed during the various stagesin making; hence, the successful makermust follow closely by some means theacid formation in the curd until it is putto press.

It is very necessary that the milk shallcontain a sufficient number of acid-forming bacteria to produce therequired amount of acid. If a sufficientnumber of bacteria are not present inthe milk as it is received, as is the case

with very sweet milk, they must beadded by the maker in the form of astarter, or the process of making willbe much prolonged.

FIG. 35.—BACTERIA IN CHEESE.A photomicrograph of curd just after

curdling has taken place. Note thefew lactic acid bacteria embedded in

the curd.

Starters in cheese making. Thestarters used in cheese making, areidentical with those employed in buttermaking and the same precautionsshould be observed in theirpropagation. It is important that thestarters should not be such as to form ahard curd that cannot be mixeduniformly with the milk, since the curdparticles would appear as white specksin the cheese. The starter should beadded to the milk through a hair sieve,and well mixed with the milk, so as to

distribute the bacteria uniformly.Amounts varying from 0.5 to 2 per centare used. In butter making, it isessential that the bacteria of the starterbe able to form not only acid, butsufficient flavor-forming substances toimpart to the butter a desirable flavor.In cheese making it is not probable thatthis latter characteristic is of anyparticular importance.

FIG. 36.—BACTERIA IN CHEESE.A photomicrograph of curd at the

time the salt is added. The lactic acidbacteria have increased materially in

numbers.

It is desirable that the process ofcheese making shall conform as closelyas possible to that which experiencehas shown to give the best results. Therate at which acid is developed in thecurd and the rapidity with which thewhey is expelled therefrom should beara certain ratio to each other. If the milkhas too high a degree of acidity, i.e., isoverripe, the acidity developed in thecurd will be too high before the curd issufficiently firm; with a very sweetmilk, the reverse may be true. It isdesirable for the cheesemaker to obtainas good an idea as possible of thecondition of the milk with reference toits bacterial content, since this willdetermine the rate at which acid will be

formed in the curd. If the milk is toosweet, i.e., too low in acid-formingbacteria, a starter should be added. Theonly methods by which thisinformation can be obtained by themaker is by determining the acidity bythe usual method or better by the use ofthe rennet test by which is ascertainedthe time required for a given amount ofrennet to curdle a definite quantity ofmilk at a standard temperature. Thevarying factor in the test will be theacidity of the milk. Very slightdifferences influence profoundly thetime of curdling. If, working understandard conditions, it is found that thetime of curdling of one sample is 10seconds and of another sample, 20

seconds, it is proof that the acidity ofthe first is higher than that of thesecond, that its bacterial content isgreater and that acidity will develop inthe curd more rapidly. The first mayneed a small amount of starter, thesecond a larger quantity. Working withmilk from the same source, the maker,from his experience, will know howmuch starter should be added to milkthat has given a certain result with therennet test in order that the acid shallbe developed in the curd at a desiredrate.

Ripening of cheese. The curd at thetime it is put to press is tough andrubbery, and has none of thecharacteristic flavor of cheddar cheese;

it is also quite insoluble andindigestible. Before the cheese is fit toeat it must pass through a complexseries of changes which arecollectively known as ripening. Inthese changes there is not only abreaking down of the casein intosoluble compounds, which processmakes the cheese soft and plastic underpressure, but the characteristic flavor isdeveloped in greater or less degree. Avery considerable part of the cheesethus becomes soluble in water, and it ismuch more easily digested than in anunripened condition.

The different factors that are operativein the ripening changes are not yetfully known, but in recent years as a

result of scientific study, materialprogress in the study of the changes hasbeen made.

Rennet. The commercial rennet extractwhen in condition for use contains veryfew bacteria. A preservative, boricacid, is added by the manufacturer torestrain the bacteria, otherwise theextract would soon be unfit for use.The bacteria in the commercial rennetextract are too few to be of anyimportance whatever in the ripeningprocess.

Rennet extract contains an enzyme,rennin, that causes the milk to curdle;also another enzyme, pepsin, thatexerts a digestive action on the curdled

casein. Pepsin is always found in thestomach juices of all animals, but nodigestive action takes place, unless thereaction is distinctly acid, as is the easeunder normal conditions, sincehydrochloric acid is excreted by thewalls of the stomach. Outside of thestomach, the same conditions mustobtain with reference to the presence ofacid, if pepsin is to exert a digestiveeffect. In the cheese curd, the milksugar is rapidly changed into lacticacid by the action of the bacteria. Thisgives the proper chemical reaction forpeptic action, and the enzyme is thenable to act on the paracasein, thenitrogenous part of the cheese. If milkcontains no acid-forming bacteria,

conditions will not permit of pepticaction, and as a consequence, theripening processes do not take place. Ifthe sugar is fermented by someorganism that does not form acid, asthe lactose-fermenting yeasts, thecheese does not ripen. The lacticbacteria are therefore an essentialfactor in inaugurating the ripeningchanges in all types of rennet cheese.

Preservative action of acid. In aprevious chapter it was shown that rawmilk does not undergo putrefactionbecause of the restraining effect of theacid formed by the lactic bacteria onthe putrefactive organisms. This samephenomenon is noted in cheese. Milkalways contains putrefactive bacteria

which pass into the cheese, but theycannot grow therein because of thehigh acidity. In the absence of the acid-forming organisms in the cheese, thecheese may remain tough and rubbery,on account of the lack of suitableconditions for the action of the pepsinof the rennet extract, or when the milkcontains large numbers of digestingorganisms, the cheese may develop aputrefactive condition, as noted by theoffensive odor and soft pasty texture.

Other factors concerned in cheeseripening. There are other factors thatare also concerned in the complexseries of ripening changes noted incheddar cheese. All animal fluids andtissues, if kept under perfectly sterile

conditions at ordinary temperatures,will undergo a certain amount ofdecomposition, due apparently to theircontent in enzymes that have adigestive action. Meat kept in storagebecomes more tender due to thesoftening of the connective tissue.Milk, derived as it is from activelysecreting cell tissue, gives certainreactions that are common to livingmaterial. If chloroform, which restrainsthe action of bacteria, but does notprevent the activity of enzymes, isadded to it, it will curdle in the courseof a few weeks and will becomepartially digested. This digestingferment found in milk is known asgalactase. Compounds are formed in

milk thus preserved that are similar tothose found in a ripe cheddar cheese.Many experiments have been madewith pasteurized milk, but it has notbeen possible to produce typical,normal cheese from thoroughlypasteurized milk. Such cheese aremarkedly deficient in the typical flavorof cheddar cheese. From this fact it isbelieved that the inherent enzymes ofmilk are a factor of some importance inthe ripening of this type of cheese atleast, if not of all types.

In the past, other factors have beenthought to be of importance. Duclaux, aFrench bacteriologist, considered thatthe enzymes formed by the digestingbacteria are responsible for the

ripening. It is now known that they canhave but little if any part in theprocess, since they are not present inall cheese in sufficient numbers to haveany marked effect, and since theacidity of the cheese mass will notpermit of their development.

Other types of bacteria have beenconsidered by bacteriologists to be ofimportance in the ripening process, butit is certain that the purely digestivechange in the mass of the cheese can beaccounted for through the action of thefactors already noted.

Flavor production. The flavor of anytype of cheese is the most importantcharacteristic, just as it is in butter, for

it is largely the flavor that determinesthe selling value of the product, and isthe most difficult thing to control. Ithas been thought that the flavor-producing substances were derivedfrom the paracasein of the curd andwere produced by the factors that areconcerned in the digestion of theparacasein. It has been shown that acheese may be thoroughly ripened asfar as its physical properties areconcerned; that it may contain the endproducts of casein digestion, and yet below in flavor. From recent researches itseems probable that the production offlavor is connected with the changethat the sugar undergoes in the acidfermentation, as volatile acids, acetic,

formic, etc., as well as alcohols andesters are formed in increasingamounts as the ripening progresses.These may have come from thedecomposition of the milk sugar, orfrom a secondary change in theproducts of the lactic fermentation.There are organisms in both milk andcheese that do not grow on the ordinaryculture media used by thebacteriologist, and it may well be thatsome of these are of importance inflavor production. Their destruction inpasteurization is likely to be one of thereasons for the failure of cheese madefrom pasteurized milk to developtypical flavor.

Effect of temperature on ripening.

The temperature at which the ripeningcheese is kept has been found to be ofthe greatest importance in determiningthe quality of the product. If the cheeseis kept at high temperatures, theripening proceeds rapidly; the cheese isshort lived, and has a sharp, strongflavor, and generally a more or lessopen texture. Unless the cheese is madefrom the best quality of milk, it islikely to undergo undesirablefermentations when ripened at hightemperatures.

Within recent years it has been foundpossible to ripen cheese attemperatures that were previouslythought to be certain to spoil theproduct. Much of the cheese is now

ripened at temperatures below 50° F.The ripening goes on more slowly thanat higher temperatures, but the flavorof the cheese is clean and entirelydevoid of the sharp undesirable tangthat is so frequently noted in oldcheese, and the texture is solid andmeaty. Ripening at low temperatures,when the milk is not of the best quality,is certain to result in a much betterproduct than when higher temperaturesare employed.

Abnormal fermentations in cheese.As has been previously shown, it isnecessary to have an abundant supplyof acid-forming bacteria in the milkfrom which cheese is to be made. Ifthese bacteria are supplanted by other

kinds, the product will be more or lessabnormal either in texture or in flavor,or possibly in both. Many of theseabnormal fermentations have beenstudied and the organisms concerned inthe changes found.

If the milk is handled carelessly, it willcontain many bacteria able to formacid and gas. As noted previously,these organisms form products in milkthat have an offensive odor and adisagreeable taste. In cheese the gasescause the formation of holes, more orless numerous, depending on thenumber of the gas-forming bacteria inthe milk. Where these bacteria areabundant, gas may appear while thecurd is in the vat, causing it to float in

the whey, when it is known as a"floater." Again, the gas may notbecome evident until the cheese is inthe press or on the curing shelf, when itbecomes apparent by the swelling orbulging of the cheese. Such cheese istermed "huffed" or "swelled." Theinternal pressure may be so great as tocause the cheese to crack and to forceout some of the curd. The presence ofgas holes is indicative of a poor cheese,because the formation of gas is alwaysaccompanied by the presence of otherundesirable compounds.

Pure culture starters are often used toovercome gassy fermentations. Incheese a certain amount of acid can beproduced by the acid-forming bacteria.

When the pure lactic bacteria alone arepresent, the cheese is very likely to beof good quality. If the sugar isfermented by gas-forming organisms,the curd will be full of holes and theflavor poor, while if the sugar isfermented by a mixture of the desirableand undesirable bacteria, the quality ofthe product will depend on the relationof the two types. If through theaddition of a pure-culture starter, theproportion of desirable bacteria isincreased, the gas will be lessened inamount and the cheese improved. Itwas formerly supposed that the lacticbacteria had an injurious effect on thegas-forming organisms. There is nogood reason to believe that this is the

case, but that both grow in the milk andcheese, but since only a certain amountof acid can be produced, it is importantto have as much of it formed by thelactic bacteria as possible, since theamount of injurious products in thecheese will thus be limited.

FIG. 37.—GASSY CHEESE.Such a cheese is worthless on accountof its poor flavor. The irregular holes

are mechanical. The crack on theupper side is due to the pressure of

the gas which has caused the cheeseto bulge at this point.

The gas formed in the curd before thecheese is put to press can be gotten ridof by proper manipulation of the curd.While this treatment may improve theappearance of the cheese, it does noteliminate the substances that impart tothe cheese undesirable qualities.

Gassy curds have also been treated bywashing the curd with cold water. Caremust be taken in applying this methodfor the removal of too much of thesugar and acid from the curd by thewashing will permit the growth ofinjurious forms of bacteria. Theaddition of salt or of saltpeter has also

been made to the milk in order toovercome gassy conditions in the milk.In the handling of gassy milk, the usualpractice has been to develop a largeramount of acid before drawing thewhey than in the case of good milk.This was done with the idea that acidsuppressed gas formation. It has beenshown previously that this is not thecase. It has also been shown by Doanethat the development of too much acidbefore drawing the whey is likely toresult in undesirable flavors, producingwhat is known as "high-acid" or "sour"cheese.

The gas-forming bacteria grow best athigh temperatures; hence, cheese keptunder these conditions are more likely

to be affected by this trouble than arethose kept at lower temperatures.

The most successful method ofpreventing trouble with gassy milk incheese making is to eliminateundesirable milk by frequent testing ofthe supply of the different patrons bymeans of the Wisconsin curd test.

Not only gas-forming bacteria may bethe cause of gassy cheese, but thelactose-fermenting yeasts may causesimilar trouble. If these are abundant inthe milk, a considerable part of thesugar may be fermented by them, inwhich case, carbon dioxide gas isabundantly formed. The cheese thusrendered gassy will present the same

appearance to the eye as where the gasis formed by bacteria, but will have adifferent flavor. The odor of alcoholmay be evident, and if most of thesugar has been fermented by the yeast,the acidity of the cheese may not besufficient for the pepsin to exert itsdigestive action.

Milk containing many gas-formingbacteria occurs most frequently insummer. It is claimed by some that themilk of cattle pastured on low lands ismore likely to contain the gas-formingorganisms than that from cattle runningon higher lands. If this is true, it mustbe due to the bacterial content of thesoil; the udders of the animals becomesoiled as they lie on the ground, and

during the milking, the dust finds itsway into the pail. Many cheese makersthink that the milk from an animalsuffering from a garget may be thecause of the huffing of cheese. Thisbelief is undoubtedly well founded, assome of the bacteria known to be thecause of garget are gas-forming.

Bitter cheese. In a previous chapter thebitter fermentation of milk has beendiscussed. If milk containing largenumbers of such organisms is madeinto cheese, the bitterness is very likelyto be noted in it. Cheese made frommilk containing few or no lacticbacteria is likely to develop a bittertaste, due to the growth of the digestivebacteria that are able to grow through

the lack of acid in the cheese.

If the milk contains considerablenumbers of yeasts, a sweet or fruityflavor is apt to develop, due to theproducts of the fermentation of thesugar by the yeast. This flavorresembles that of fermented fruit, orthe bouquet of certain kinds of wine.

Putrid cheese. In the absence of acid-forming bacteria, the cheese maydevelop a putrid or rotten odor, due tothe growth of some types ofputrefactive or digesting bacteria. Thistrouble is very infrequent in cheddarcheese, since this is made from ripenedmilk, but occurs more frequently inthose types in which no acid is

developed.

Bacteria develop in the cheese incolonies or masses, just as they do inthe plate cultures of the bacteriologist,made with transparent media, such asgelatin. Cheese is opaque; therefore,the growing colonies cannot be readilydiscovered, but when pigment-formingbacteria grow in the cheese, theirpresence is likely to be noted, becauseof the colored spots that are formed.

Rusty spot. The "rusty spot" that hasbeen encountered in New York andCanada is due to one of the coloredbacteria which produces an orange oryellowish-red pigment. Various otherpigment-forming organisms have been

met in cheese, each producing itscolored colony which differentiatesitself from the mass of the cheese. Ifthe pigment is produced inconsiderable quantities, and is solublein any of the constituents of the cheese,the color will not appear in spots butwill be more diffuse, or may impart acolor to the entire mass.

Cases of acute poisoning arising fromthe ingestion of cheese are notinfrequently reported; similar instancesresult from the use of ice cream. Inboth cases it is believed that poisonousproducts have been formed by bacteria,probably by some of the putrefactiveforms.

From what has been said with referenceto the abnormal fermentations ofcheese, it will be seen that they arealways due to the lack of acid-formingbacteria, or to their partial replacementby other types. In order to prevent suchtroubles, it is necessary to insure thatthe milk has been produced under cleanconditions, from healthy cows, and hasbeen handled in such a manner as toreach the maker in as sweet and freshcondition as possible. The maker can,by the use of proper starters, controlthe kinds of bacteria essential for theripening process. A well trained makershould be able to prepare from suchmilk a uniform product of the highestquality. The effort of cheese makers at

the present time is to handle milk ofmore or less objectionable quality so asto secure from it as good cheese as ispossible. But cheese is so sensitive asto character of milk used that greatereffort should be spent in securing animproved supply.

Moldy cheese. In the case of thecheddar cheese and other types of hardcheese, it is essential that their surfacesbe kept clean, and not discolored by thegrowth of molds, which find favorableconditions for growth on the surface ofthe cheese in the moist atmosphere ofthe curing room. The molding ofcheddar cheese can be prevented bycovering the cheese with a layer ofparaffin which stops the development

of the mold spores, by shutting off thenecessary supply of oxygen. For thispurpose the cheese are dipped inmelted paraffin when a few days old.

In the case of types of cheese which aresalted by applying the salt to thesurface, or with soft cheese which ripenfrom the outside, other methods ofmold prevention are employed, such asrubbing and washing the cheese. Thecuring room itself may be freed fromthe mold spores by the use of suchstandard disinfectants as formalin orsulphur.

Swiss cheese. One of the mostimportant kinds of hard cheese, is theSwiss or Emmenthaler, so named, from

the country and valley in which thecheese was first made. In America, thistype was introduced by Swissimmigrants, and is being made inconstantly increasing quantities inOhio and Wisconsin.

Swiss cheese is a hard firm type,appearing in the markets in the form ofthe flat circular "drum" cheese, two tothree feet in diameter, and six to eightinches thick, or in the smaller "block"form. In this country the cheese isprepared twice a day, since it isnecessary to work up the milk while itis perfectly sweet. Indeed, the milk isreceived at the factories while it is stillwarm, and within five or six hours afterit is drawn from the cow the cheese is

on the press. If the attempt is made toprepare Swiss cheese from the kind ofmilk that is best suited for cheddarpurposes, i.e., milk in which the acidityhas increased to some extent, the flavorof the resulting product is likely toapproximate a cheddar cheese ratherthan that of a Swiss.

In the salting process, the salt is notmixed with the curd before it ispressed, but is applied by immersingthe cheese for a few days in a saturatedbrine, and then rubbing salt over thesurface of the cheese. In this way thesalt gradually diffuses quite uniformlythrough the cheese. The method ofsalting has apparently a markedinfluence on the ripening process, since

if the salt is added in the same way,and in amounts used in the cheddarprocess, the flavor will not be that of aSwiss cheese but will resemble acheddar.

In cheddar cheese, the whey is expelledfrom the curd by means of the acidwhich is developed in the curd, and byheating the curd to a temperature of95° F. to 100° F. In Swiss cheese thedevelopment of acid during the makingprocess is prevented, because of thesmaller number of acid-formingbacteria in the milk; other factors musttherefore contribute to the expulsion ofthe whey to secure a firm curd. This isaccomplished by cutting the curd intovery small pieces and by briskly

stirring it during the making, heating itduring this process for a period of 20 to30 minutes at 130° to 140° F. It mightbe thought that this high temperature,which is approximately that used inpasteurization would destroy the acid-forming bacteria, but these areapparently protected as they are withinthe curd. During the time the cheese isbeing pressed, the contained bacteriabegin to grow and the whey comingfrom the cheese toward the end of thepressing shows a high acidity. If it doesnot show such a development of acid,the maker has reason to believe that thecheese may never ripen in a typicalmanner.

It has been mentioned that the milk

contains but few acid-forming bacteria.The maker, however, attempts to insurethe presence of a sufficient number bythe use of "home-made" rennet. This isprepared by placing a piece of driedrennet, i.e., the stomach of the calf, inwhey, keeping the same in a warmplace for twenty-four to thirty-sixhours. As the rennet contains acid-forming organisms, these grow rapidlyin the warm whey, so that by addingthis sour whey to the milk, the maker isnot only adding rennet, that is to curdlethe milk, but also a small starter oflactic bacteria. If the rennet thusprepared contains no harmful bacteriaand the milk is of good quality, thecheese is likely to ripen in a normal

manner. The rennet should be preparedwith due regard to bacteriologicalprinciples, a condition that is rarelymet in Swiss factories in this country.

Swiss cheese has two strikingcharacteristics, the flavor and thepresence of holes or "eyes." The flavoris sweetish rather than the sharp andpungent flavor of cheddar cheese. Thebacteria concerned in its production arenot known, but it is certain that specificorganisms play some role, since if theflora of the cheese is changed bysalting the curd or by the use of milkcontaining large numbers of lacticbacteria, the flavor will also bechanged. This role of the acid-formingbacteria in Swiss is the same as in

c h e d d a r , i.e., through the acid,conditions are established for pepticaction, the curd being partially digestedwhile at the same time the curd mass isprotected from putrefactive processes.

In Swiss cheese during the ripeningprocess, holes about the size of a largecherry develop which should be quiteuniformly distributed throughout thecheese. The inner surface of the hole isglistening and, in a well-ripenedcheese, a small quantity of clear brine,i.e., "tears" may be noted. These holesor "eyes" may be called the trade markof the Swiss cheese, since without themthe product has a lessened commercialvalue, even if it possesses the typicalflavor. The "eyes" are caused by

bacteria that ferment the lactic acidproduced by the lactic bacteria,forming from it propionic acid andcarbon dioxide, the latter gas being thecause of the hole or "eye."

FIG. 38.—SWISS CHEESE.Normal development of "eyes" in aSwiss cheese. The eyes are generally

as large as a cherry.

The "eye"-forming organisms cannotgrow in the presence of any amount ofsalt, hence, if salt is added directly tothe curd, the cheese is likely to be"blind" or free from holes. The eyes areformed not at the time gas holes areproduced in a cheddar cheese, i.e.,early in the ripening process, but after

a lapse of three or four weeks. They aremost abundant in the middle of thecheese since the manner of salting issuch as to inhibit their formation nearthe surface. The eye-forming bacteriamay have some effect on the flavor ofthe cheese.

The Swiss maker encounters the sametroubles as does the cheddar maker.Gassy cheese is more prevalent in theSwiss than in the cheddar industry,since the maker cannot call to his aidthe methods used by the cheddarmaker, viz., the addition of a heavystarter, the washing of the curd, etc. Itis especially important that the qualityof the milk be first class in everyrespect, and yet customs prevail in the

Swiss industry that are directlyinimical to the production of goodmilk. The grossest carelessnessprevails at the factories in the matter ofhandling the whey. It is often kept inindividual barrels for each patron. (SeeFig. 8.) These are not kept thoroughlyclean and the result is that the wheytaken back to the farm in the cans thatare used to bring the fresh milk is oftenin an advanced stage of fermentation.

There are many other kinds of hardcheese; but in each, so far as is known,the role of the acid-forming bacteria isidentical with that noted in cheddar andSwiss cheese, viz, in preparingconditions favorable for peptic action,and preventing the development of

putrefactive bacteria present in thecurd.

Roquefort cheese. Among the moreimportant foreign types of cheese thatare characterized by the developmentof mold is Roquefort, so named fromthe district in France in which it ismade. This cheese is made fromsheep's milk, in much the same manneras cheddar. The characteristic processin its preparation is the inoculation ofthe curd, at the time it is put to press,with the spores of a particular kind ofmold, a type closely related to theordinary green mold of bread andcheese. The mold for inoculation isgrown on bread, the whole mass beingdried so that it can be powdered; then

the ground-up material is sprinkled onthe curd as it is placed in the presshoops. The first stage in the ripening ofRoquefort is probably identical withthat of the types of hard cheesesalready considered, the breaking-downof the curd being due to the pepsin ofthe rennet used, which action is madepossible by the acid formed by thebacteria.

The second stage in ripening, and onein which the characteristic flavor of thecheese is developed, is due to thegrowth of the mold with which thecheese is seeded. Molds can grow onlyin the presence of air, and in order toprovide this condition, the cheese arerun through a machine having a series

of needle-like projections which fillsthe cheese with fine holes. This allowsthe air to penetrate the cheese and themold to grow, the fruiting of whichdevelops the characteristic flavor. Thechanges produced by the mold are notwell understood, but the flavor isevidently connected with itsdevelopment since in the absence ofmold, it does not appear. The cheesemust be cured under carefullycontrolled conditions, as totemperature and moisture; in Francethese are secured by curing the cheesein limestone caves that are highlysaturated with moisture. Attempts havebeen made to make Roquefort cheesein other parts of the world, but they

have never been successful, dueundoubtedly to the fact that the properenvironment and conditions for thedevelopment of the various types oforganisms necessary in the ripeningprocess have not been met. This cheeseis sold for 50 to 75 cents per pound inthe markets of the world.

There are two other kinds of cheesethat are closely related to Roquefort, asto the manner of ripening, viz., theGorgonzola of Italy and the Stilton ofEngland, both of which possess theircharacteristic flavors by reason of thedevelopment of molds. In Stiltoncheese the mold is not intentionallyadded, the maker relying on thecontamination that comes from the

factory for the usual seeding. If thisdoes not develop, it is sometimesinoculated by exchanging plugs with awell-ripened Stilton. This method isnot so certain as in the inoculation ofRoquefort.

Camembert cheese. A typical exampleof soft cheese is one of the Frenchtypes, known as Camembert. Thischeese is prepared from cow's milkwhich is curdled by rennet. The curd isnot cut but is dipped into the forms,which condition, taken with theabsence of pressure in forming thecheese, accounts for the large quantityof whey in it. The finished cheese areabout one inch in thickness and threeinches in diameter. In the ripening, the

moisture and temperature of the curingroom are very carefully regulated.

The first stage in the ripening is due tothe rennet and the lactic bacteria. Laterthere appears on the surface of themoist cheese, a moldy growth. In this,there are at least two kinds of molds,the ordinary mold that appears on sourmilk, Oidium lactis, and another that isrelated to the bread mold but which hasa white instead of a green fruitingstage. These molds are confined to thesurface of the cheese but the enzymeswhich they produce diffuse into thesubstance, changing the color from adull, opaque white to a translucentyellow. The acid that has been formedby the lactic bacteria is gradually used

up by the growth of the mold, andconditions then become favorable forthe growth of putrefactive bacteriawhich digest the curd. The cheese isready for use when the action of themold has penetrated to the center of thecheese, and before any pronouncedputrefaction has taken place. Theproduction of the typical flavor isdependent upon there being a definiterelation between the growth of themolds and bacteria. This relation isdependent largely upon the moistureand temperature of the curing room.These cannot always be regulated withexactness; and hence, much of this typeof cheese is not of first quality, andmust be sold for a low price. While

such fancy cheeses, as Camembert,bring fifty cents and upward per pound,and the yield from the milk is muchgreater than with the hard type ofcheese, yet the difficulties ofsuccessful manufacture are such as tomake success less easily attained thanwith the other types.

There are many other kinds of softcheese that depend for their ripeningupon factors similar to those concernedin the ripening of Camembert; most ofthem are, however, of smallimportance from a commercialstandpoint.

Limburger cheese. A very famouscheese is one originally made in

Germany to which the name Limburgeris given. It is classed as a soft cheesealthough it is much firmer thanCamembert. This cheese is made fromcow's milk and is pressed very lightlyor not at all, which condition accountsfor its high per cent (50 per cent) ofmoisture. The surface is kept moist byrepeated washing of the cheese, and bykeeping the air of the curing room verymoist. A yellowish, slimy, bacteriallayer soon develops on the surfaceunder these conditions. The enzymesproduced by this external growthgradually diffuse to the center of thecheese, when it is regarded as ripe. Theodor of the matured product issomewhat putrefactive, but is not so

offensive as is usually supposed.

Definite knowledge concerning thetypes of organisms concerned in thesurface layer is very limited. It is notcertain whether the same kinds oforganisms must always be present.Limburger is much easier to make thanCamembert, due possibly to the factthat there are not needed definite formsof life and that the balance betweenthem is not so delicate.

A cheese known as brick is closelyrelated to Limburger in its method ofmaking and of ripening but is lesspronounced in flavor.

In the manufacture of all of these types

of cheese, troubles are likely todevelop, due to an abnormal bacterialcondition of the milk.

It will be seen from what has been saidthat the bacteria are essential factors incheese ripening, and that the cheeseindustry, like the butter industry, maybe called a true fermentation industry.Close co-operation must exist betweenthe milk producer, and the maker sothat the type of fermentation that goeson in the milk can be controlled. Arecognition of the fundamentalprinciples governing thesefermentations, both normal as well asabnormal, is now regarded as anessential part of the training of thedairy manufacturer of today.

CHAPTER IX.

BACTERIA IN MARKETMILK.

Within the last decade attention hasbeen especially directed toward thequality of milk that is furnished to thepeople in the cities. This has comeabout, in part, in connection with thedemands made for better and purerfood of every kind. These demands arereflected in the pure-food laws enactedby the federal government, and by thevarious states and municipalities.

Another factor that has focusedattention on the milk supplies has beenthe belief that it plays an importantrole in the production and distributionof disease, especially among children.The rapid growth of cities in all of thegreat countries of the world, the higherstandard of living, and the greaterdemand for milk and other dairyproducts, has, of necessity, widened thezone from which the milk supply ofany particular city must be drawn. Milkis now an article of export and ofimport; some of the great cities draw aportion of their supply from farmshundreds of miles away. This meansthat a longer time must elapse betweenthe time of production and

consumption, necessitating the exerciseof greater care in production andhandling in order to preserve the milkuntil it reaches the consumer.

In the past in the cities, as in thesmaller towns at present, the supplywas largely furnished by the producerdirectly to the consumer. This directcontact afforded the consumer theopportunity of informing himself of theconditions under which his milk supplywas produced if he desired. The adventof the middleman in the business, andthe gathering of the milk from manyhundreds of farms, and itsredistribution to thousands of homeshas made it impossible for theindividual consumer to learn anything

of the conditions surroundingproduction. When the individual cannotprotect himself against fraud andunhealthful conditions, it is the duty ofthe government to protect him. This isthe theory underlying the moderncontrol of food supplies, watersupplies, and of living conditions ingeneral. Acting on this basis the citiesare seeking to control, to an increasingdegree, the healthfulness andcleanliness of the milk supply.

Formerly such control as was givenwas largely with reference to thecomposition of the milk, theregulations providing that it shouldcontain not less than a minimumamount of fat and other solids, and be

free from preservatives. The moremodern regulations are much morecomplex and touch every phase ofproduction and handling that can, inany way, affect the value of the milk ashuman food.

Municipal regulations. The differentcities vary widely in the methodsemployed to secure a satisfactory milksupply. Rules and regulations areadopted to which the producer anddealer must conform. In order toascertain whether the regulations arebeing obeyed, two types ofexaminations may be made: first theinspection of the farms and of theplants of the dealers; second theexamination of the milk itself with

reference to its chemical composition,bacterial content and temperature.

The city of New York is doing more tosafeguard and to improve its milksupply than any other large city in thiscountry. A brief summary of itsregulations and methods follow. Acopy of the rules is furnished to eachdairyman and is supposed to be postedin the stable.

The Cows.

1. The cows must be kept clean, andmanure must not be permitted tocollect upon the tail, sides, udder andbelly of any milch cow.

2. The cows should be groomed daily,and all collections of manure, mud orother filth must not be allowed toremain upon their flanks, udders orbellies during milking.

3. The clipping of long hairs from theudder and flanks of the cows is ofassistance in preventing the collectionof filth which may drop into the milk.The hair on the tails should be cut, sothat the brush will be well above theground.

4. The udders and teats of the cowshould be thoroughly cleaned beforemilking; this to be done by thoroughbrushing and the use of a cloth andwarm water.

5. To prevent the cows from lyingdown and getting dirty betweencleaning and milking, a throat latch ofrope or chain should be fastened acrossthe stanchions under the cow's neck.

6. Only feed which is of good qualityand only grain and coarse fodderswhich are free from dirt and mouldshould be used. Distillery waste or anysubstance in a state of fermentation orputrefaction must not be fed.

7. Cows which are not in good fleshand condition should be immediatelyremoved and their milk kept separateuntil their health has been passed uponby a veterinarian.

8. An examination by a veterinarysurgeon should be made at least once ayear.

The Stable

9. No stagnant water, hog-pen, privy oruncovered cesspool or manure pitshould be maintained within 100 feetof the cow stable.

10. The cow stable should be providedwith some adequate means ofventilation, either by the constructionof sufficient air chutes extending fromthe room in which the cows are kept tothe outside air, or by the installation ofmuslin stretched over the windowopenings.

11. Windows should be installed in thecow barn to provide sufficient light (2sq. feet of window light to each 600cubic feet of air space the minimum)and the window panes be washed andkept clean.

12. There should be at least 600 cubicfeet of air space for each cow.

13. Milch Cows should be kept in aplace which is used for no otherpurpose.

14. Stable floors should be made water-tight, be properly graded and welldrained, and be of some non-absorbentmaterial. Cement or brick floors are thebest, as they can be more easily kept

clean than those of wood or earth.

15. The feeding troughs and platformsshould be well lighted and kept clean atall times.

16. The ceiling should be thoroughlyswept down and kept free from hangingstraw, dirt and cobwebs.

17. The ceiling must be so constructedthat dust and dirt therefrom shall notreadily fall to the floor or into the milk.If the space over the cows is used forstorage of hay, the ceiling should bemade tight to prevent chaff and dustfrom falling through.

18. The walls and ledges should bethoroughly swept down and kept free

from dust, dirt, manure or cobwebs,and the floors and premises be keptfree from dirt, rubbish and decayinganimal or vegetable matter at all times.

19. The cow beds should be so gradedand kept that they will be clean andsanitary at all times.

20. Stables should be whitewashed atleast twice a year unless the walls arepainted or are of smooth cement.

21. Manure must be removed from thestalls and gutters at least twice daily.This must not be done during milking,nor within one hour prior thereto.

22. Manure should be taken from thebarn, preferably drawn to the field.

When the weather is such that thiscannot be done, it should be stored notnearer than 200 ft. from the stable andthe manure pile should be so locatedthat the cows cannot get at it.

23. The liquid matter should beabsorbed and removed daily and at notime be allowed to overflow or saturatethe ground under or around the cowbarn.

24. Manure gutters should be from sixto eight inches deep, and constructed ofconcrete, stone or some non-absorbentmaterial.

25. The use of land plaster or lime isrecommended upon the floors and

gutters.

26. Only bedding which is clean, dryand absorbent should be used,preferably sawdust, shavings, driedleaves or straw. No horse manureshould be used as bedding.

27. The flooring where the cows standshould be so constructed that allmanure may drop into the gutter andnot upon the floor itself.

28. The floor should be swept daily.This must not be done within one hourprior to milking time.

29. If individual drinking basins areused for the cows, they should befrequently drained and cleaned.

30. All live stock other than cowsshould be excluded from the room inwhich the milch cows are kept. (Calf orbull pens may be allowed in the sameroom if kept in the same clean andsanitary manner as the cow beds.)

31. The barnyard should be welldrained and dry, and should be as muchsheltered as possible from the wind andcold. Manure should not be allowed tocollect therein.

32. A suitable place in some separatebuilding should be provided for the useof the cows when sick, and separatequarters must be provided for the cowswhen calving.

33. There should be no direct openingfrom any silo or grain pit into the roomin which the milch cows are kept.

The Milk House.

34. A milk house must be providedwhich is separated from the stable anddwelling. It should be located onelevated ground, with no hog-pen,privy or manure pile within 100 feet.

35. It must be kept clean and not usedfor any purpose except the handling ofmilk.

36. The milk house should be providedwith sufficient light and ventilation,with floors properly graded and made

water-tight.

37. It should be provided withadjustable sashes to furnish sufficientlight and some proper method ofventilation should be installed.

38. The milk house should be providedwith an ample supply of clean water forcooling the milk, and if it is not arunning supply, the water should bechanged twice daily. Also a supply ofclean ice should be provided to be usedfor cooling the milk to 50 degreeswithin two hours after milking.

39. Suitable means should be providedwithin the milk house, to expose themilk pails, cans and utensils to the sun

or to live steam.

40. Facilities consisting of wash basins,soap and towel should be provided forthe use of milkers before and duringmilking. During the Summer Monthsthe Milk House should be properlyscreened to exclude flies.

The Milkers and Milking.

41. Any person having anycommunicable or infectious disease, orone caring for persons having suchdisease, must not be allowed to handlethe milk or milk utensils.

42. The hands of the milkers must bethoroughly washed with soap and

water, and carefully dried on a cleantowel before milking.

43. Clean overalls and jumpers shouldbe worn during the milking of thecows. They should be used for no otherpurpose, and when not in use should bekept in a clean place protected fromdust.

44. The hands and teats should be keptdry during milking. The practice ofmoistening the hands with milk is to becondemned.

45. The milking stools should be at alltimes kept clean, and iron stools arerecommended.

46. The first streams from each teat

should be rejected, as this fore milkcontains more bacteria than the rest ofthe milk.

47. All milk drawn from the cows 15days before, or 5 days after parturitionshould be rejected.

48. The pails in which the milk isdrawn should have as small an openingat the top as can be used in milking;top opening preferably not to exceed 8inches in diameter. This lessens thecontamination by dust and dirt duringmilking.

49. The milking should be done rapidlyand quietly, and the cows should betreated kindly.

50. Dry fodder should not be fed to thecows during or just before milking, asdust therefrom may fall into the milk.

51. All milk utensils, including pails,cans, strainers, and dippers, must bekept thoroughly clean and must bewashed and scalded after each using,and all seams in these utensils shouldbe cleaned, scraped and soldered flush.

The Milk.

52. Milk from diseased cows must notbe shipped.

53. The milk must not be in any wayadulterated.

54. The milk as soon as drawn shouldbe removed to the milk house andimmediately strained and cooled to theproper temperature.

55. All milk must be cooled to atemperature below 50 degrees F.,within two hours after being drawn,and kept thereafter below that untildelivered to the creamery.

56. The milk should be strained intocans which are standing in ice waterwhich reaches the neck of the can. Themore rapidly the milk is cooled, thesafer it is, and longer it will keepsweet. Ice should be used in coolingmilk, as very few springs are coldenough for the purpose.

57. If aerators are used, they shouldstand where the air is free from dust orodors, and on no account should theybe used in the stable or out of doors.

58. Milk strainers should be kept clean;scalded a second time just beforeusing, and if cloth strainers are used,several of them should be provided, inorder that they may be frequentlychanged during the straining of themilk.

59. The use of any preservative orcoloring matter is adulteration, and itsuse by a producer or shipper will be asufficient cause for the exclusion of hisproduct from the City of New York.

Water Supply.

60. The water supply used in the dairyand for washing utensils should beabsolutely free from anycontamination, sufficiently abundantfor all purposes, and easy to access.

61. This supply should be protectedagainst flood or surface drainage.

62. The privy should be located notnearer than 100 feet of the source ofthe water supply, or else be providedwith a water-tight box that can bereadily removed and cleaned, and soconstructed that at no time will thecontents overflow or saturate thesurrounding ground.

63. The source of the water supplyshould be rendered safe againstcontamination by having no stable,barnyard, pile of manure or othersource of contamination located within200 feet of it.

In order that the farm inspection shallbe as effective as possible, and to makethe work of the several inspectors asuniform as may be, the dairies arescored. A copy of the score cardfollows.

DEPARTMENT OFHEALTH

The City of New York

Division of GeneralSanitary Inspection

Dairy Report

Inspection No.___Time___A. P. M.Date______191__

1. Dairyman___________Owner__________

2. P. O.Address___________ P.O. Address______State____

3. County_______State____ PartyInterviewed________

4. Milk delivered to

Creamery at_____Formerly at_____

5. Operated by________Address____________

6. Distance of farm fromCreamery____ Occupiedfarm since____

7. No. Cows____ No.Milking____ No. Qts.Produced____

8. All persons in thehouseholds of thoseengaged in producing orhandling milkare_____free from allinfectious disease.Weekly reportsare_____being filed

9. Date and nature of lastcase onfarm___________

10. WATER SUPPLY forutensils is froma_______located____feet deep andapparently is______pureand wholesome______State any possiblecontamination locatedwithin 200 feet ofsource of water supplyor if water supply is notprotected againstsurface drainage

11. Water supply on thisfarm

analyzed____191__Result______

12. Style of CowBarn___Length___ft.Width___ft. Height ofceiling___ft.

13. Dairy Rules of theDepartment of Healthare_____posted_______

14. Dairy Herd examinedby________on_________191__Report______

PERFECT ALLOW

EQUIPMENT15 COW STABLE

is______located onelevated groundwith no stagnantwater, hog-pen,privy, uncoveredcesspool or manurepit within 100 feet 1

16 FLOORS, otherthan cow beds, areof concrete or somenon-absorbentmaterial

2

17 Floorsare______properlygraded and water-tight 2

18 Cow bedsare______of

concrete or plankslaid on concrete 2

19 DROPSare.....constructedof concrete, stoneor some non-absorbent material 2

20 Drops are......water-tight and spacebeneath is clean anddry 2

21 CEILING isconstructedof______and istight and dust proof 2

22 WINDOWSNo______total

square feet thereis______2 squarefeet of window lightfor each 600 cu. ft.air space (1 sq. ft.per each 600 cu. ft.—1) 2

23 VENTILATIONconsistsof______sq. ft.muslin in ceilingor______which issufficient 3, fair 2,poor 1, insufficient0 3

24 AIR SPACEis______cu. ft. percow (600 and over

—3) (500 to 600—2) (400 to 500—1)(under 400—0) 3

25 LIVE STOCK,other than cows,are______excludedfrom rooms inwhich milch cowsare kept 2

26 Thereis______directopening from stableinto silo or grain pit 1

27 Separate quartersare______providedfor cows whencalving or sick 1

28 COW YARDis______properlygraded and drained

2

29 WATER SUPPLYfor cowsis______unpollutedand plentiful 1

30 MILK HOUSEhas______directopening into cowbarn or otherbuilding 1

31 Milk househas______sufficientlight and ventilation 1

32 Flooris______properly

graded and water-tight

1

33 Milk houseis______properlyscreened to excludeflies

134 Milk pails

are______ofsmoothly tinnedmetal in good repair 1

35 MILK PAILShave______allseams solderedflush 2

36 Milk pailsare______of thesmall mouthed

design, top openingnot exceeding 8inches in diameter.Diameter

2

37 Racksare______providedto hold milk pailsand cans when notin use

238 Special milking

suitsare______provided 1

40PERFECT ALLOW

METHODS39 STABLE

INTERIOR painted

or whitewashedon______which issatisfactory 3, fair 2,unsatisfactory 1,never 0 3

40 FEEDINGTROUGHS,platforms or cribsare______welllighted and clean 1

41 Celling is______freefrom hanging straw,dirt or cobwebs 3

42 Window panesare______washed andkept clean 1

43 WALLS ANDLEDGES

are______free fromdirt, dust, manure orcobwebs 2

44 FLOORS ANDPREMISESare______free fromfrom dirt, rubbish ordecayed animal orvegetable matter 2

45 COW BEDSare______clean, dryand no horse manureused thereon 2

46 Manureis______removed tofield daily 4, to atleast 100 feet frombarn 2, stored less

than 100 feet orwhere cows can get atit 0 4

47 Liquid Matteris______allowed tosaturate ground underor around cow barn 2

48 Milking stoolsare______clean 1

49 Cow Yardis______clean andfree from manure 2

50 COWShave______beentuberculin tested andall tuberculous cowsremoved 7

51 Cows are______all ingood flesh andcondition at time ofinspection 2

52 Cows are______allfree from clingingmanure and dirt. (No.dirty ____) 4

53 LONG HAIRSare______kept shorton belly, flanks,udder and tail 1

54 UDDER ANDTEATS of cowsare______thoroughlybrushed and wipedwith a clean damp

cloth before milking 355 ALL FEED

is______of goodquality and distillerywaste or anysubstance in a state ofputrefactionis______fed

256 MILKING

is______done withdry hands 2

57 FORE MILK or firstfew streams fromeach teatis______discarded 2

58 Clothing of milkersis______clean 1

59 Facilities for washinghands of milkersare______provided incow barn or milkhouse

260 Milk is strained

at______and______inclean atmosphere 1

61 Milk is______cooledwithin two hours aftermilking to 50 degreesF. 3, to 55 degrees F.2 to 60 degrees F. 1 3

62 Ice is______used forcooling milk 1

63 MILK HOUSEis______free from

dirt, rubbish and allmaterial not used inthe handling andstorage of milk 1

64 Milk utensilsare______rinsed withcold waterimmediately afterusing and washedclean with hot waterand washing solution 2

65 Utensilsare______sterilizedby steam or boilingwater after each using 2

66 Privy is______insanitary condition,with vault and

seats______coveredand protected 1

60

Remarks

Equipment 40 per cent. Score ....percentMethods 60 per cent. Score ....per centPerfect Dairy 100 per cent. Score ....percent

A copy of the completed report is leftwith the dairyman.

Before the farm inspection is carriedout the creameries to which the milk isdelivered by the farmers are inspectedat the time the milk is being delivered.

The temperature of the milk and itscleanliness are noted. In the creamerythe straining, cooling and handling ofthe milk are observed as well as thewashing of the milk cans and otherutensils, and the construction andcondition of the creamery, theopportunity for the water supply tobecome contaminated, and the presenceof infectious diseases among theemployees.

Grades of milk. Three grades of milkhave been established. Each dealer isrequired to state which grade or gradeshe expects to handle. Thespecifications for the different gradesare as follows.

Grade A. Guaranteed Milk. Guaranteedmilk is that produced at farms holdingpermits therefor from the Departmentof Health and produced and handled inaccordance with the followingminimum requirements, rules andregulations:

1. Only such cows shall be admitted tothe herd as have not re-acted to adiagnostic injection of tuberculin.

2. All cows shall be annually testedwith tuberculin, and all re-actinganimals shall be excluded from theherd.

3. No milk from re-acting animals shallbe shipped to the City of New York for

any purpose whatever.

4. The milk shall not contain more than30,000 bacteria per c. c. when deliveredto the consumer, or at any time prior tosuch delivery.

5. The milk shall be delivered to theconsumer only in sealed bottles, whichhave been sealed at the dairy.

6. The milk shall be delivered to theconsumer within 30 hours of the timeat which it was drawn.

Grade A. Certified Milk. Certified milkis milk certified by a milk commissionappointed by the Medical Society ofthe County of New York, or theMedical Society of the County of

Kings, as being produced under thesupervision and in conformity with therequirements of that commission aslaid down for certified milk, and soldunder a permit therefor issued by theBoard of Health.

No milk shall be held, kept, offered forsale, or sold and delivered as certifiedmilk in the City of New York which isproduced under requirements less thanthose for guaranteed milk.

Grade A. Inspected Milk—Raw.Inspected milk (raw) is milk producedat farms holding permits therefor fromthe Board of Health, and produced andhandled in accordance with thefollowing minimum requirements,

rules and regulations:

1. Only such cows shall be admitted tothe herd as have not re-acted to adiagnostic injection of tuberculin.

2. All cows shall be tested annuallywith tuberculin, and all re-actinganimals shall be excluded from theherd.

3. No milk from re-acting animals shallbe shipped to the City of New York forany purpose whatsoever.

4. The farms at which the milk isproduced must obtain at least 75 pointsin an official score of the Departmentof Health. These 75 points shall bemade up as follows: A minimum of 25

points for equipment, and 50 points formethod.

5. The milk shall not contain more thanan average of 60,000 bacteria per c. c.when delivered to the consumer, or atany time prior thereto.

6. Unless otherwise specified in thepermit, the milk shall be delivered tothe consumer only in bottles.

Grade A. Selected Milk—Pasteurized.Selected milk (pasteurized) is milkproduced at farms holding permitstherefor from the Board of Health, andproduced and handled in accordancewith the following requirements, rulesand regulations:

1. The farms at which the milk isproduced must obtain at least 60 pointsin an official score of the Departmentof Health. Of these 60 points, aminimum of 20 points shall be requiredfor equipment and a minimum of 40points for method.

2. All milk of this grade shall bepasteurized, and said pasteurizationshall be carried on under a specialpermit issued therefor by the Board ofHealth, in addition to the permit for"Selected Milk (Pasteurized.)"

3. The milk shall not contain more thanan average of 50,000 bacteria per c. c.when delivered to the consumer, or atany time after pasteurization and prior

to such delivery.

4. Unless otherwise specified in thepermit, the milk shall be delivered tothe consumer only in bottles.

5. All containers in which pasteurizedmilk is delivered to the consumer shallbe plainly labeled "Pasteurized."Labels must also bear the date and hourwhen pasteurization was completed,the place where pasteurization wasperformed, and the name of the person,firm or corporation performing thepasteurization.

6. The milk must be delivered to theconsumers within 30 hours after thecompletion of the process of

pasteurization.

7. No milk shall be pasteurized morethan once.

8. No milk containing in excess of200,000 bacteria per c. c. shall bepasteurized.

General Regulations for Grade A—

1. The caps of all bottles containingmilk of Grade A shall be white, andshall contain the words "Grade A" inblack letters, in large type.

2. If cans are used for the delivery ofmilk for Grade A, the said cans shallhave affixed to them white tags, withthe words "Grade A" printed thereon in

black letters, in large type, togetherwith the designation "Inspected Milk(Raw)" or "Selected Milk(Pasteurized)," as the quality of thecontents may require.

Grade B. Selected Milk—Raw. Selectedmilk (raw) is milk produced at farmsholding permits therefor from theBoard of Health, and produced andhandled in accordance with thefollowing minimum requirements,rules and regulations:

1. Only such cows shall be admitted tothe herd as have been physicallyexamined by a regularly qualifiedveterinarian and declared by him to behealthy, and free from tuberculosis in

so far as a physical examination maydetermine that fact.

2. The farms at which the milk isproduced must obtain at least 68 pointsin an official score of the Departmentof Health. These 68 points shall bemade up as follows: A minimum of 25points for equipment, and a minimumof 43 points for method.

3. The milk shall not contain anexcessive number of bacteria whendelivered to the consumer, or at anytime prior thereto.

Grade B. Pasteurized Milk. Pasteurizedmilk (Grade B) is milk produced undera permit issued therefor by the Board

of Health, and produced and handled inaccordance with the followingminimum requirements, rules andregulations and in further accordancewith the special rules and regulationsrelating to the pasteurization of milk.

1. The milk after pasteurization mustbe at once cooled and placed insterilized containers, and the containersimmediately closed.

2. All containers in which pasteurizedmilk is delivered to the consumer shallbe plainly labeled "Pasteurized".Labels must also bear the date and hourwhen the pasteurization wascompleted, the place wherepasteurization was performed, and the

name of the person, firm or corporationperforming the pasteurization.

3. The milk must be delivered to theconsumer within 36 hours after thecompletion of the process ofpasteurization.

4. No milk shall be pasteurized morethan once.

5. No milk containing an excessivenumber of bacteria shall bepasteurized.

General Regulations for Grade B—

1. Caps of bottles containing milk ofgrade B shall be white and marked"Grade B" in bright green letters of

large type.

2. The necks and shoulders of canscontaining grade B milk shall bepainted bright green, and a metal tagshall be attached to each can with thewords "Grade B" in large type, and thewords of the subdivision to which thequality of the milk in said canconforms.

Grade C. Grade C is to be used forcooking and manufacturing purposesonly. It includes all raw milk that doesnot conform to the requirements of anyof the subdivisions of grade A or gradeB.

1. The caps of all bottles containing

milk of grade C shall be white andshall contain in red the words "GradeC" in large type and "for cooking" inplainly visible type.

2. Cans containing milk of grade Cshall be painted red on necks andshoulders and shall have in red thewords "Grade C" in large type and thewords "for cooking" in plainly visibletype affixed to each can.

All creameries handling milk ofdifferent grades will be required todemonstrate to the Department ofHealth that they are capable of keepingthe grades separate, and must keeprecords satisfactory to the Departmentof Health concerning the amount of

milk of each grade handled each day.

It is to be noted that the grades of milkare based on the bacterial content ofthe milk and on the opportunity for themilk to become contaminated withpathogenic organisms. From thestatements made in a previous chapterit is evident that the number of bacteriain any sample of milk is dependentupon (1) the original amount ofcontamination, (2) the age of the milk,and (3) the temperature at which it hasbeen held. A high bacterial content isindicative of poor milk, while a lowbacterial content can be obtained, inthe case of raw milk, only where dueattention is paid to cleanliness andcooling. This relation between the

quality of milk and its bacterial contenthas led many cities to adopt numericalbacterial standards, even when gradesof milk have not been established.Boston requires that the milk shall notcontain more than 500,000 bacteria percubic centimeter. Rochester, N. Y., hasa standard of 100,000 per cubiccentimeter, while Chicago requires thatthe milk on arrival in the city shall notcontain more than 1,000,000 per cubiccentimeter from May first toSeptember thirtieth, and not over500,000 between October first andApril thirtieth. The sale of milkcontaining more than 3,000,000bacteria per cubic centimeter isprohibited.

It has been urged that bacterialstandards are not of value since thehealthfulness of milk depends on thekind of bacteria present rather than onthe number. It is well recognized thatmilk containing millions of acid-forming organisms, butter milk, is ahealthful food, while that containingmany less bacteria may contain somedisease-producing organisms. It hasbeen urged that a qualitative standardshould supplant the quantitative. Theconsumer desires milk that has beenproduced under clean conditions, andwhich has good keeping qualities. Theharmless forms of bacteria exert thegreatest influence on the keepingquality. Experience has shown that the

quantitative examination of the milksupply as it comes from the farm is themost feasible method of determining,in the laboratory, whether the farmerhas obeyed the rules with reference tocleanliness and cooling of the milk.The bacteriological examination alsogives an indication as to whether thelarge number of bacteria is due to grosscontamination of the milk with mudand manure, or actual growth ofbacteria as in old milk. In the lattercase the ordinary acid-forming bacteriawill usually predominate in the milk,while in the former, the number ofkinds of bacteria and the proportionbetween the kinds will be changed. It isof course evident that the quantitative

standards should be applied withjudgment.

It is also claimed that the delay insecuring the results in the quantitativeexamination of milk is an objection tothe bacterial standard, since the milk isconsumed before the laboratoryfindings can be obtained. It is true thatit does not protect the community asfar as the particular sample isconcerned, but it is also true that theexamination is not made for thepurpose of determining the conditionof the particular sample, so much as itis to determine the methods that areemployed on any particular farm, andthese do not vary widely from day today. Thus, if a number of samples give

high results, it is evident thatconditions surrounding productionneed investigation.

If the milk is well cooled on the farm,and kept cold while being shipped, thegrowth of bacteria will be slow, and thecondition of the milk as far as keepingquality is concerned, much better thanif less care is used. Some cities havetemperature standards; New Yorkrequires that the milk shall be cooled to50° F. on the farm, and shall not beabove 50° F. on arrival in the city.Others require that it shall not be above50° F. on delivery to the consumer.

Certified milk. In many cities theMedical Societies have appointed Milk

Commissions, that adopt rules andregulations, concerning the productionof milk that shall receive the certificateof the commission. Producers, whodesire to have their milk thus certified,must satisfy the commission that theyare able to conform to the rules. Thecommission appoints a physician toexamine the personnel of the farm, aveterinarian to make frequentexaminations of the herd, a chemist toexamine the milk as to its contents infat and other solids, and abacteriologist to determine thebacterial content of the milk. The rulesare very stringent and cover everypoint that may influence, in any way,the value of the milk as human food. In

order to conform to these requirements,a heavy expenditure must be incurred,and the business must pay for suchexpert service; hence, certified milkmust be sold at high prices, twelve totwenty-five cents per quart. This pricemakes it a special product and its use isconfined mainly to infant feeding.

The bacterial standard for certifiedmilk is usually 10,000 bacteria percubic centimeter. It is only by theexercise of the greatest care at everypoint that the bacterial content can bekept below this maximum.

The term "certified milk" has beenregistered by Mr. Francisco of NewJersey, who was the first to engage in

the production of such milk under thedirection of the Medical MilkCommission of Essex County, NewJersey. The use of the term is allowedwhen the milk is produced under theregulation of any Medical MilkCommission.

Most certified milk is now produced onfancy dairy farms conducted bywealthy men. The barns and otherequipment are the best that can beobtained, and the methods employed,as far as cleanliness is concerned, areextreme. In some of the dairies thebacterial content is reduced to a fewhundred per cubic centimeter, or to thatwhich is derived from the interior ofthe udder. Such milk will, when well

refrigerated, keep for long periods oftime. It is a not uncommon thing forsuch milk to keep perfectly sweet forten to fifteen days.

Tests for the quality of milk. At themilk depot and elsewhere, it isfrequently desired to determine thebacterial condition of the milk in a lessrefined manner than by the platecultures of the bacteriologist, whichrequire a large amount of time for theirpreparation and do not yield anypositive information for at leasttwenty-four hours. There are a numberof such tests that may be applied.

FIG. 39.—SEDIMENT TESTERS.In the use of the apparatus on the

right, increased air pressure is usedto hasten the filtering process; the

same is accomplished in the

apparatus shown in the center bywarming the milk by the injection of

steam between the walls of thedouble jacket.

1 . Dirt or sediment test. This is madeby filtering a pint of the mixed milkthrough a small disc of absorbentcotton. The insoluble dirt is retainedand imparts a color to the cotton, theshade of which is dependent on theamount of dirt (P. 45). Since it isimpossible to have dirt withoutbacteria, it is evident that milkscontaining a large amount of dirt willbe high in bacteria. The reverse,however, is not necessarily true.

FIG. 40.—GOOD MILK.A plate culture inoculated with 1/100

of a cubic centimeter of milkcontaining 67 colonies, which equals6,700 bacteria per cubic centimeter

of milk. Such milk will keep well.

2. Acidity test. The acidity of the milkis also an indication of its bacterialcontent. If the acidity has increased,above the normal for fresh milk, thebacterial content is certain to be high,and the keeping quality poor. Anacidity above 0.2 per cent in marketmilk is to be avoided, as an increase inacidity is always preceded by a greatincrease of bacteria.

Whether the acidity is above or belowthis point can be rapidly and easilydetermined at the receiving station by amodification of the Farrington acidtest. Dissolve one alkaline tablet in anounce of water. A unit volume of this

solution added to a unit volume of milkis equal to 0.1 per cent of acidity. Iftwo measures are provided,—one forthe alkaline solution holding just twiceas much as that used for the milk, theapproximate acidity can be quicklydetermined by mixing a measure ofeach in a common white cup. If theacidity is above 0.2 per cent the colorwill remain white; if a pink colordevelops, it indicates an acidity lessthan this amount. This test is alsouseful in the selection of milk or creamthat is to be used for special purposes,such as pasteurization.

FIG. 41.—POOR MILK.A plate culture inoculated with1/1000 of a cubic centimeter ofmarket milk containing 1,680

colonies, which equals 1,680,000bacteria per cubic centimeter. Such

milk has poor keeping qualities.

3 . Alcohol test. A test giving similarinformation is made by adding twoparts of 70 per cent alcohol to one partof milk, and noting whether curdlingoccurs.

4. Curd test. The curd test described onp. 100 gives no indication of thenumber of bacteria present, onlyconcerning the types present. It hasbeen proposed to combine thefermentation test with the reductiontest referred to below and thus gainsome idea of, not only the number, butthe kinds of bacteria present.

5. Reduction test. The reduction test ismade by adding to twenty cubiccentimeters of milk, one-half cubiccentimeter of a solution of methyleneblue, a coal tar dye. A saturatedsolution of the dye is made in alcohol,and 2.5 per cent of this solution addedto water. The time required for thereduction of the dye or the change ofthe color from blue to white when thesamples are placed in tubes and kept at98 to 100° F., is dependent upon thenumber of bacteria present. Byallowing the tubes to stand untilcurdling occurs, and noting the natureof the curd, whether the solid curd ofthe desirable acid-forming bacteria orthe gassy curd of the harmful types is

produced, knowledge is gained of thekinds of bacteria present.

According to Barthel, milks that reducethe methylene blue within fifteenminutes contain hundreds of thousandsof bacteria per cubic centimeter. Thosethat require from fifteen minutes to onehour for the disappearance of the colorare also high in bacteria, and are to beclassed as a poor grade of market milk.If one to three hours is required, themilk is comparatively low in bacteria,and is to be classed as a good grade ofmarket milk. When more than threehours elapse before the disappearanceof the blue color, the bacterial contentis low and the milk is to be placed inthe highest grade.

The time of reduction is only a roughindex of the number of bacteriapresent, but it gives a good idea of thekeeping quality of the milk, and of theconditions of production and handling.Of the above tests the sediment andacid tests are more frequently used.

Examination of milk sediments. Inthe modern municipal laboratory,efforts are made to determine, as far aspossible, the conditions of productionon the farms, by an examination of themilk in the laboratory. The samples ofmilk are sedimented in a smallcentrifuge, and an examination of thesediment made with the microscope.The types of bacteria and the numberof body cells found is an indication as

to whether any of the animals of theherd are suffering from inflammationof the udder. The test also givesinformation similar to the dirt testsince the insoluble dirt will be throwndown and will impart a color to thesediment.

Pasteurization of market milk..Thespread of the pasteurizing process asapplied to market milk has been rapid.This has been due to the recognition ofthe fact that only by this process can asafe milk i.e., one free from pathogenicbacteria, be obtained. As previouslymentioned a small proportion of allhuman beings that have suffered fromtyphoid fever become bacillus carriers.It is impossible to examine all persons

who may be concerned in the handlingof milk in order to ascertain whetherthey belong to this dangerous andunfortunate class of people.

The larger cities have also recognizedthe impossibility of requiring thetuberculin test of all cattle furnishingmilk. Pasteurization remains the onlysafeguard, and it is probable that withina short time all the larger cities willrequire the pasteurization of all milk,except that produced under strictsupervision.

As previously mentioned heatingcauses certain changes in milk. In thetreatment of market milk it is desirableto use as low temperatures as will

suffice to destroy the disease-producing bacteria. It is fortunate thattemperatures that will insure this resulthave little effect on the milk. Thetemperatures now recommended forpasteurization are as follows:

158 degrees F. for 3 minutes.155 degrees F. for 5 minutes.152 degrees F. for 10 minutes.148 degrees F. for 15 minutes.145 degrees F. for 18 minutes.140 degrees F. for 20 minutes.

In actual practice the milk is heated to145 degrees for 25 to 30 minutes. Theacid-forming bacteria are notcompletely destroyed and thepasteurized milk as a rule will undergo

the same type of fermentation as rawmilk. It is, however, deemed essentialthat all pasteurized milk be sold assuch; that it be delivered to theconsumer within twenty-four hoursafter pasteurization and that no milk bepasteurized a second time.

The continuous pasteurizing machineshave the disadvantage that a smallportion of the milk passes through soquickly that all pathogenic bacteriatherein might not be destroyed, (p.131). This has led to the use of the"holding" process in which the milk isheated to the desired temperature andthen placed in tanks where it remains atthis temperature for any desired time.Every portion is thus treated in a

uniform manner.

If the milk is bottled afterpasteurization, there remainsopportunity for reinfection, possiblywith typhoid bacilli. Pasteurization inthe final container, the bottle, is beingrecommended. This is possible onlywhen a special bottle is used with ametal cap lined with paper.

Milk distribution. Until within recentyears in the cities and at present insmaller towns, milk is largely retailedfrom cans which are carried on thewagons or are kept in stores. Thisexposes the milk to contaminationfrom street dust and from the containerfurnished by the consumer. It is well

recognized that every utensil withwhich milk is brought in contact addsmore or less bacteria to it, and the lessmilk is handled, the better will be itscondition when it reaches theconsumer. Milk is now largely retailedin glass bottles which are closed withpulp caps. In some cities the bottling ismainly done in the country at thebottling station to which the milk isbrought by the farmers; or it may beshipped by the producer to adistributing company, and allsubsequent treatment, as pasteurizationand bottling done in the city.

Milk plants are now generally equippedfor the rapid and economical handlingof large quantities of milk in a most

sanitary manner. The bottles as theyare returned from the consumer arewashed in a continuously-actingautomatic washer which washes, rinsesand sterilizes the bottles without theirbeing removed from the cases in whichthey are carried on the wagons. Thesemachines are effective, if not run at toorapid a rate, so that the bottles are notexposed for a sufficiently long periodof time to sterilize them. The bottlesare then filled and the paper capsinserted by machinery. The caps cannow be obtained from themanufacturers in sealed tubes in whichthey have been sterilized so that thecontamination from this source isavoided. The shipping cans are washed

and sterilized with live steam, and inmany plants are thoroughly dried, bypassing hot air into them. Under theseconditions they then reach the farmerwith none of the musty anddisagreeable odor that frequently ispresent when the can contains a smallquantity of water, condensed fromsteam.

The top of the milk bottle over whichthe milk is poured is exposed tocontamination from the hands of thedeliveryman. Trouble from this sourcecan be avoided if the consumer cleansthe lip of the bottle before removingthe cap. The better grades of milk aredispensed in bottles, the top of which isprotected by an additional cover of

paper or tin foil which reaches to theneck of the bottle and is held in placeby a crimped metal band.

Milk supply of the small cities. It istrue that the quality of milk supplied tothe large cities by the great milkcompanies is generally much superiorto that sold in the smaller cities andvillages. Many of the smaller placesare however, attempting in variousways to improve their supply. It isevident that methods will be successfulhere that can not be employed in thelarger places. A detailed and carefulfarm inspection by a tactful, capableinspector, coupled with properpublicity will do much to improveconditions. The publication of the

scores of the different farms, and thedemonstration of the sediment test asapplied to their product attractsfavorable attention to the good dairiesand unfavorable attention to the poor.This usually has an effect on the tradesufficient to cause the negligentproducer and dealer to improve.

It is also becoming recognized thathigh grade milk can be produced withvery simple equipment. In fact thesmall farm is often more successful inproducing high grade milk than is thelarge farm on which the work must bedone by hired help for here thepersonality of the owner can not makeitself felt as where the producer isdoing a portion of the work about the

barn and dairy himself. It is becomingmore and more evident that the chieffactor in the production of clean milkis the personality of the producer; heshould be one who gets enjoyment outof his clean stables and cows and hishigh grade product.

The man who is producing milk for thecity market is but one of many and hisindividual efforts can not makethemselves felt. The dairyman who ismarketing his own product is in aposition where his efforts to produce afine product should prove of distinctadvantage to him in enabling him tosell it for a higher price than thatobtained for ordinary milk.

It should be remembered that theproduction of clean, healthful milk isnot a question of equipment, but ofmethods and of additional work. Thecows must be fed, the stables must becleaned, the cows milked, and the milkdelivered to the consumer. If beyondthis unavoidable labor a smalladditional amount is expended, theimprovement in the product will begreat. It is necessary that the additionalwork be placed where it will do themost good, in keeping the cows cleanboth summer and winter so that littleneed be done in cleaning them beforemilking, the pails and other utensilskept clean and sterilized, and the milkcooled as soon as possible and kept

cold until delivered to the consumer.The delivery should be made within theshortest practicable time after the milkis drawn. In order that the healthfulnessof the milk may be beyond question,the herd must be kept free fromtuberculosis and some attention shouldbe paid to the health of the men,especially with reference to whetherthey may be typhoid carriers or not.The necessary labor should notincrease the cost of the milk over onecent per quart. It has been shown inmany cases that such a product can bemarketed at a price that will more thancompensate for the additional cost.Clean, fresh, rich milk is being sold invillages and small cities located in the

great butter and cheese producingsections of the country for eight to tencents per quart.

The duty of the consumer. Theeducational campaign that has beencarried on by the health departmentswith reference to farm conditions andmethods of handling has been mosteffective in improving the milk supply.Many cities are now extending this tothe consumer, recognizing that as muchharm may be done in the home as onthe farm. The importance of keepingthe milk cold, of not allowing it tostand exposed in open vessels, ofthoroughly cleaning the vessel in whichit is kept, or the milk bottle beforereturning it to the milkman are

especially emphasized.

Moreover, it must be impressed uponthe consumer that all of theseimprovements, not only on the farmwhere the milk is produced, but in thehands of the distributing companies inthe cities, involve much expense, andcannot be carried out, unless theconsumer is willing to pay their cost.More objection seems to be raised overan increase in the price of milk thanany other food stuff. The consumertherefore needs education along theline of higher prices for milk. Dairyproducts of all types have increasedmuch in value in recent years, so that atpresent prices milk, sold directly asmilk, is relatively cheaper than in any

form, when prevailing prices arecompared with those that obtained adecade ago.

INDEX.Abnormal fermentations, overcomingof, 108.

Abortion, contagious, 75.

Acid, amount of formed in milk, 84.

Acidity test, 211.

Actinomycosis, 75.

Aeration of milk, 55.

Aerobic bacteria, 13.

Air, contamination of milk from, 51.

Alcohol test, 213.

Alcoholic fermentation, 96.

Anaerobic bacteria, 13.

Animal, contamination of milk from,42.

Anthrax, 75.

Antiseptics, 16, 117.

B.

Bacillus Bulgaricus, 89, 101.

Bacillus lactis acidi, 86.

Bacteria, aerobic, 13;anaerobic, 13;culture media for, 20;desirable acid-forming, 86;determining number of, 22;distribution of, 18;effect of cold on, 14;effect of heat on, 15;food of, 12;forms of, 8;manner of growth of, 9;movement of, 11;nature of, 8;

parasitic, 11;products of, 17;pure cultures of, 25;rate of growth of, 13;relation to air, 13;relation to chemicals, 16;relation to drying, 15;relation to light, 16;relation to temperature, 12;size of, 9;saprophytic, 11;spores of, 10;types of acid-forming, 86;undesirable acid-forming, 90.

Bedding, 47.

Bitter fermentation, 97.

Bleaching powder, 112.

Bloody milk, 99.

Butter, bacteria in, 154;bacterial defects in, 156;cowy odor in, 157;deterioration of, 155;fishy, 157;metallic, 157;molding of, 157;preservatives in, 155;putrid, 156;source of flavor, 140;turnip flavored, 156;types of, 137.

Butter-milk, 100.

Butyric fermentation, 93.

Boric acid, 117.

Borax, 117.

C.

Carbolic acid, 111.

Cheese, abnormal fermentations of,174;

bitter, 177;Camembert, 186;Cheddar, 164;

colored, 178;flavor production in, 172;gassy, 174;Gorgonzola, 185;Limburger, 187;moldy, 179;preservation of by acid, 171;putrid, 178;quality of milk for, 162;ripening of, 169;Roquefort, 184;Stilton, 185;Swiss, 180;temperature of ripening, 173;types of, 161.

Children, diseases of, 80.

Chloride of lime, 112.

Cholera, 80.

Cleaning utensils, 39.

Clean milk, production of, 53.

Cold, effect of, on bacteria, 14.

Colored milk, 98.

Condensed milk, 135.

Contagious abortion, 75.

Contamination of milk, from milkingmachine, 50;

in factory, 59.

Cooling of milk, 54.

Corrosive sublimate, 111.

Cream, control of fermentation of, 142;pasteurization of, 146;ripening of, 138;separators, 36.

Cresol, 111.

Curd test, 104.

Cycle of fermentations, 99.

D.

Deodorants, 109.

Digestive fermentation, 93.

Diphtheria, 79.

Dirt, exclusion of, 44;removal of from milk, 53.

Disinfectants, 16, 109.

Disinfection, 109.

Distribution of bacteria, 18.

Dried milk, 135.

Drugs, excretion of in milk, 58.

Drying, effect of on bacteria, 15.

E.

Emmenthaler cheese, 180.

Evaporated milk, 134.

F.

Factory by-products, 36;treatment of, 38.

Feeds, effect of on milk, 57.

Fermentation test, 104.

Fermented milks, 100.

Fly, contamination of milk by, 60;means of spreading typhoid fever,

78.

Foot and mouth disease, 74.

Fore milk, 31; rejection of, 34.

Formalin, 112.

G.

Galactase, 172.

Garget, 75.

Germicidal action of milk, 33.

Gorgonzola cheese, 185.

H.

Hairs, bacteria on, 43.

Heat, effect on bacteria, 15.

Heated milk, detection of, 39.

Hydrogen peroxide, 118.

K.

Kefir, 102.

Koumiss, 102.

L.

Lange Wei, 95.

Light, effect on bacteria, 16.

Limburger cheese, 187.

Lime, 110.

Lumpy jaw, 75.

M.

Malta fever, 75.

Market milk, municipal regulationsconcerning, 190;

pasteurization of, 214.

Milk, acid fermentation of, 83;aeration of, 55;affected by feed, 57;alcoholic fermentation of, 96;bacterial standards for, 206;

bitter fermentation of, 93;certified, 202;butyric fermentation of, 93;certified, 202, 208;clarifying of, 115;condition of when secreted, 29;contamination of from animal, 42;from by-products, 36;from utensils, 34;contamination of with tubercle

bacilli, 67;cooling of, 54;creaming of, 136;culture medium for bacteria, 28;cycle of fermentation in, 99;distribution of, 216;digestive fermentation of, 93;dirt in, 44;

effect of heat on, 119;filtration of, 114;germicidal action of, 33;grades of, 201;guaranteed, 201;inspected, 202;miscellaneous fermentations of, 98;pasteurization of, 120;pasteurization of in home, 131;preservation of by antiseptics, 117;preservation of by cold, 116;relation to children's diseases, 80;ropy fermentation, 94;sediments, examination of, 214;selected, 203;slimy, 94;spontaneous fermentation of, 91;sterilization of, 134;

straining of, 153;supply of small cities, 217;sweet curdling fermentation of, 92;tainted, 56, 58;temperature standards for, 208;tests for quality of, 209.

Milk pails, sanitary, 48;small topped, 48.

Milker, factor in contamination ofmilk, 51.

Milking-machines, 36, 50.

Mold on butter, 177;on cheese, 179.

O.

Odors, absorption of, 56, 58.

Oidium lactis, 186.

Oleomargarine, 152.

P.

Pasteurization, 120;efficiency of, 133;purpose of, 123;methods of, 125.

Pasteurized milk, fermentations in,124.

Pasteurizing machines, tests of, 130.

Process butter, 152.

Ptomaine poisoning, 81.

Pure cultures, 25.

R.

Rabies, 75.

Reduction test, 213.

Rennet, 170.

Ropy fermentation, 94.

Roquefort cheese, 184.

Rusty spot in cheese, 178.

S.

Salicylic acid, 117.

Scarlet fever, 79.

Score card for dairies, 198.

Sediment test, 210.

Skim milk, heating of, 38.

Slimy fermentation, 94.

Spores of bacteria, 10.

Stalls, 46.

Starters, 143;for cheese, 167;propagation of, 146.

Sterilization, 21, 134.

Stilton cheese, 185.

Storch test, 39.

Straining of milk, 33.

Sulphur, 111.

Sweet curdling of milk, 92.

Swiss cheese, 180.

T.

Taints, determination of cause of, 58,103.

Temperature effect on growth, 12.

Tubercle bacilli, destruction of, 71;in butter, 70;in cheese, 70;

in milk, 67.

Tuberculin test, 73.

Tuberculosis, 64;closed, 70;distribution of disease in animal, 66;economic aspects of, 72;open, 70.

Typhoid fever, 76.

U.

Udder, inflammation, 75;invasion of by bacteria, 30;number and kind of bacteria from,

32;structure of, 30;washing of, 47;cleaning of, 39.

Utensils, contamination from, 34.

W.

Water, effect on butter, 153;supply, 59;testing of, 60.

Whey, heating of, 38.

Wisconsin curd test, 104.

Y.

Yeast fermentation, 96.

Yoghurt, 101.

End of the Project Gutenberg EBook of

Outlines of dairy bacteriology, by

H. L. Russell and E. G. Hastings

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