ciliary action - thorax · ciliary action there is an active stroke, followed by a passive recoil....

Thorax (1949), 4, 57.

CILIARY ACTIONBE

V. E. NEGUSLondon

INTRODUCTIONTo those interested in diseases of the chest,

ciliary action should be of absorbing interest, notonly through its importance in the interpretationand treatment of inflammatory infections, but alsofrom its intrinsic physiological fascination.

It is surprising that physicians place so muchstress on the value of cough and so little on thatof ciliary action; the former is really a patho-logical phenomenon, while the latter is an every-day and normal means of protection. And again,those dealing with respiratory diseases shouldnever lose sight of the dependence on cilia in thephysiological processes of the nose and sinuses,with a corresponding danger when the mechanismis upset, the upper air passages then becoming asource of danger instead of a means of protectionof the lower air tracts.

HISTORICALAt a meeting held at the Royal Society of Medi-

cine in 1934, the subject of ciliary action was dis-cussed, and the writer suggested that it.should belooked on as a centenary celebration; for in 1834a comprehensive and illuminating article waswritten by Sir William Sharpey in Todd's " Cyclo-poedia of Anatomy and Physiology," published in1835. Here were described the shape and size ofcilia, their mode of action, and their response todisturbing influences. References were made toearlier writings of Purkinje and Valentin, pub-lished in 1834.To define the ciliary pathways, Sharpey inserted

charcoal into the antra and trachea of rabbits, andpreceded researches repeated in later years.

In 1895 St. Clair Thomson and R. T. Hewlettpublished an article on the defences of the upperair passages, emphasizing the importance of ciliaryaction. The subject has been further investigatedin more recent years by Gray (1920), Lillie(1906-7), Hill (1928), Lowndes Yates (1924), Proetz(1929-44, Hilding (1932, 1934), Linton (1933),Frenckner and Richtner (1940), Lucas (1931-5),and others. From the work of Proetz, in particular,much of the following information is derived.

EVOLUTION AND MODE OF ACTIONIt is of interest to consider the various purposes

to which cilia have been turned in the animaleconomy. The prototype of protoplasmic pro-truberances is to be found in pseudopodia which,in such species as Amoeba, serve for both pro-gression and the prehension of food. In theseanimalculae, as ire leucocytes, protoplasmic flowis directed in any needed direction and the broad-based projection acts in the manner of a limb. Inciliated cells, whether in unicellular organisms orin more complicated species, the cilium appears asa permanent projection, with the power of alteringits shape. It might be thought that flow of ppoto-plasm into a hollow curved tube would explain themovement, but in point of fact there is no evidenceto show that a cilium is hollow. Even so, a changein positioning of the protoplasm will lead to achange of shape, converting the resting cilium froma curved to a straight shape, and by the action, ifrapidly and forcibly executed, the transition ofshape may lead to an even extension, with a bend-ing back beyond a right angle. This is what hap-pens in ciliary action, a whip-like motion leadingto an active backward fling, with a passive recoilto the curved resting position. The movement hasbeen compared, also, to that of a fishing-rod, butin either case the analogy is not exact, since inciliary action there is an active stroke, followedby a passive recoil. The movement of propulsionis in the direction of the active stroke. The rate ofbeat is said to be 160 to 250 per minute (Frencknerand Richtner, 1940), or even up to 720 per minute(Proetz, 1929-44).

FUNCTIONSThe purposes subserved by cilia are several and

important, even though each cilium is only approxi-mately 7 u long and 0.3 ,u in diameter (Proetz).LocoMoTIoN.-A drop of stagnant pond water-

reveals Paramoecium briskly darting here andthere, propelled by a fringe of actively wavingcilia, executing a feathering stroke. Other unicellu-lar organisms have a similar means of movement.

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DEGLUTITION.-The gills of a mussel or an oysterreveal co-ordinated ciliary streams, charged withthe function of conveying particles of food to thealimentary system; vorticella shows a similaraction, .of a beautiful spiral nature. In the frogciliary streams travel along the walls of the mouthto converge at the mouth of the oesophagus; theycontinue down the lumen of the latter and arecapable of moving particles of a considerable size.RESPiRATION.-The streams of water conveyed by

the cilia of molluscs bring not only nourishment butalso oxygen to the gills; in some fish the respira-tory currents are similarly maintained.OLFACTION.-In eels, and some other fish, ciliary

action subserves the sense of smell. A stream ofwater, charged with odours or flavours, is causedto circulate over the olfactory rosette. In man,odours and flavours must go into solution beforeperception is possible; in this the ciliary streamsof mucus play a part in the olfactory area, notonly by conveying the stimulus, but also by remov-ing debris such as dust, which might otherwiseinterfere with olfaction. A similar function isserved in those carnivorous or herbivorous animalswhich rely, far more than man, on the integrity oftheir sense of smell.CLEANSING.-Cavities with rigid walls, such as

the nasal fossae and paranasal sinuses, rely onciliary action for the removal of debris and bacteriafrom their lumen; in collapsible cavities, such asthe pharynx, muscular walls are able to expel in-truding substances and no cilia are required. Itis of interest to note, however, that the upper endof the oesophagus of frogs, and the Fallopian tubein human beings, are lined by ciliated epithelium,even though they are collapsible. There are, ofcourse, limits to the powers of cilia; it may beobserved that when an object too large to bemoved is encountered, the ciliary streams passby on either side, unless obstruction is complete.Some other method of expulsion must -then befound, such as sneezing or cough; but there is acertain degree of filtering of inspired air by thehairs placed in the nasal vestibules, which cannot only prevent ingress of over-large objects intothe nose but also exclude them from the tracheo-bronchial tree if inspiration is carried on throughthe nose only and not through the mouth.

DISTRIBUTIONI[n man cilia line the greater part of the respi-

ratory tract, most of which has an ever-openlumen. But it is unnecessary for there to be a pro-vision of these propulsive agents on every part of

the mucosal surface, for, as will shortly beexplained, there is no direct action on solid par-ticles but rather a drag on the overlying coveringof mucus. It is found that there are no cilia atthe extreme anterior part of the nasal fossae-thatis, the region in front of the inferior turbinalbodies; nor are there cilia in the air vesicles oratria of the lung. In neither case is this of anydisadvantage, because the distal regions referredto can be cleared effectively by a drag on themucus covering their surfaces (Proetz, 1934).With the exclusion of the region referred to, all

the mucosa lining the nasal fossae and the para-nasal sinuses is ciliated; this motile lining extendsinto the naso-pharynx and downwards below thelevel of the Eustachian tubes as far as the upperborder of the superior constrictor muscle, whichextends well up above the soft palate.The bronchi are lined everywhere with cilia

except for the distal regions mentioned above, theatria, and air vesicles. The trachea is also com-pletely covered, but the larynx has a certaindeficiency, since the vocal folds have a squamousepithelium. This means that the only passage forsecretions conveyed by ciliary action is throughthe inter-arytenoid region; any mucus, withentangled debris and bacteria, is tipped over thisposterior lip of the larynx and is then removed byswallowing movements.

In the field of this review comes also the middle-ear tract, which has a ciliated lining, continuousthrough the Eustachian tube with that of thenaso-pharynx.

CONDITIONS AFFEcTiNG NORMAL CILIARY ACTIONMOISTURE.-Cilia cannot work alone; they do

not propel debris or bacteria directly, and cease towork if the mucosal surface becomes dry. It isessential that there should be a covering of mucus,or "blanket" as Proetz (1941) has described it.The whole mechanism may be compared to aconveyor belt or to a moving staircase or anescalator, in which the platform on which passen-gers stand or conveyed packages rest correspondsto the blanket of mucus; the propulsive agent ofunderlying pinions is represented by the cilia,which thus propel and remove deleterious particles.The blanket of mucus must be of the right vis-

cosity, sufficiently tenacious to cohere, but not sotenacious as to clog the cilia; this faculty ofcohesion enables cilia to work in relays, becausea layer of secretion can be pulled from a distance.The mucous sheet is composed of an outer stratumof mucus resting on the tips of the cilia and aninner fluid layer of low viscosity, forming a suit-

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able medium for the vibrating cilia (Lucas andDouglas, 1934).

In sinuses it is the cilia of the lining membrane,with their propulsive power, which carry secre-tions as far as the ostium, but it is apparently thedragging effect of the epithelium in the nasal fossaewhich executes the next stage of extracting secre-tions and conveying them into the naso-pharynx.-Similarly, the cilia of the terminal bronchioles cancleanse the air sacs of the lung.Not only must the viscosity of the mucus con-

form to certain criteria, but there must also be acorrect quantity, neither so great as to fill a bron-chiole or sinus, nor so deficient as to lead to stag-nation.The sensitivity of response to these alterations m

quantity may be observed in experimental animals;general anaesthesia may so diminish the totalquantity as to slow up or stop the streams, and itmay be found necessary to give pilocarpine toincrease the supply, or, alternatively to make useof decerebrate animals.The viscosity of secretions may be affected by

local applications; glycerine or oil may make ittoo thick, or potassium iodide may reduce it to toothin a consistency. In the former case there isstagnation and lack of movement, and, in thelatter, lack of concerted action.Not only does this concerted synergism between

cilia and mucus allow of cleansing of non-ciliatedareas, but it also enables rest to be afforded tocertain groups, while other cilia maintain stream-ing of the superjacent blanket (Proetz).The viscosity and quantity of secretion must be

adjusted, if the mechanism of protection is to bemaintained, in accordance with variations in theatmosphere; at high altitude or in steam-heatedrooms, the air is dry and greater calls are made onthe secretory mechanism.TEMPERATURE.-Unless extreme, variations of

temperature have little effect on ciliary action,unless of course the overlying secretion becomesfrozen or removed by desiccation (Proetz, 1934).Cilia work efficiently in the mouth of the frog andthe gills of the oyster, as well as in the trachea orbronchi of the rabbit. And in man there is nolapse in the protective mechanism, since the ciliaof the mucosa covering a mass of adenoids, or thatover nasal polypi, will continue to function afterremoval from the body. Even after death of thebody as a whole, there is a continuation of ciliarystreaming at a time when the body temperaturehas dropped to that of the atmosphere.

It may be concluded that the deleterious effectsof moderate changes of temperature are due to the

increase or reduction of mucus, and not to anydirect influence on the ciliated epithelium.

SLEEP.-If cilia continue to work after death ofthe remainder of the organism, it is no cause forsurprise that they maintain their efficiency duringsleep; there is a team action of work by relays,but no cessation of -protection.REAcTION OF MEDIuM.-There are here two

aspects to be considered; one is the medium inwhich the cilia are immersed, the other is the natureof the tissue fluids.

(a) Secretions.-To consider the former first, asbeing of the lesser importance, it is to be notedthat considerable divergencies of opinion exist asto the normal reaction of mucus, a word usedsomewhat loosely. Mucus, as applied to the secre-tions of the nose and bronchi, is a mixture madeup partly of the secretion derived from goblet cellsand racemose mucous glands, together with transu-date from the capillaries, escaping from the epithe-lial cells or through intercellular spaces togetherwith tears. The proportion of the two components iscapable of wide variation, with a consequent altera-tion in viscosity and reaction. The powers of secre-tion and transudation are so versatile as to becapable of adjusting the blanket of mucus to corre-spond with alterations of atmospheric conditions,and, in fact, the physiological variations veryeasily merge into pathological abnormalities; thisquestion will be considered later. What is inquestion at present is the reaction of the mixedsecretion.

Estimations of reaction may be carried out byvarious methods-colorimetric, electrometric, orotherwise-and the means used for testing maylead to mistakes. If nasal secretion be removedfrom the body and tested, readings of the pH areround about 7.4, but if estimations are made insitu, as described by Fabricant (1941), a lowerfigure of about 7.0 is found (see also Tweedie,1934). The matter is not of vital importance, andthe explanation of the small discrepancies is notdifficult to discover; for normal mucus containssome easily dissoluble carbon dioxide, which isreadily given off when the secretion is exposed tothe outside air. If any interval is allowed to elapse,therefore, long enough for loss of carbon dioxide,the reaction will be less acid than when the esti-mation is made in situ. There is known to be anactive excretion of carbon dioxide from the nasalmucosa; it is, in fact, a mechanism of nasal respi-ration (Hellmann, 1926). The escape of carbondioxide is said to be seven times more active fromthe nasal than from the alveolar epithelium, and

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the influence on the reaction of the nasal secretionis considerable.

Inquiry must be made as to whether these dis-crepancies of estimation have any marked physio-logical importance; unless extreme, this does notseem to be the case. Cilia work actively when ina neutral medium, and possibly rather more brisklystill when the reaction is raised, even to pH 8.5;but, on the other hand, full functional activity hasbeen observed by Proetz in ciliated epitheliumremoved from an infected maxillary sinus, in whichglycophilic bacteria, producing lactic acid, hadlowered the reaction to a pH well below 7.0.Although the reaction of the free secretions may

have an influence which is slight if moderatevariations occur, yet it is rather on the reactionsof the inter- and intra-cellular fluids that efficiencyof action depends. Mittermaier (1930) found thatthe pH of the tissues does not of necessity corre-spond with that of the secretions.

(b) Tissue fluids.-Conditions here are some-what different from those in the lumen of a sinusor bronchus. While little effect is brought to bearon the cilia themselves by changes of medium, yetmuch influence is felt when these changes affectthe tissue fluids. For the efficient nourishment ofcolumnar cells bearing cilia, two essentials mustbe satisfied; these are the correct proportion ofelements and also the correct reactions of thefluids.The supply of necessary ions has been studied

by Gray, Lillie, and others; it is found that theremust be present, in correct proportions, sodium,calcium, potassium, manganese, phosphorus, andammonium. These elements can be combined in asolution such as that of Tyrode or Ringer; ciliaryaction under experimental conditions will con-tinue almost indefinitely in these media, but if therebe any deficiency the activity gradually diminishesand finally ceases.Normal saline is often referred to as a physio-

logical solution, but it is quite inadequate to main-tain the activity of excised ciliated epithelium,which, if placed in such a medium, rapidly losesits activity and soon ceases action.On the other hand, the right admixture of ions

must be related to a correctness of reaction; thisis determined mainly by the concentration ofhydrogen ions. However little may be the effect ofalterations of pH on the cilia 'themselves, yet adifferent result is found when similar changesaffect the tissue fluids. For if excised ciliatedepithelium be kept in an artificial medium it willbe found that a rise to the alkaline side, with apH of over 8.0, tends to cause swelling of the

cells due to increased permeability of the cell walls;and in extremes the cells swell up and cease tofunction. On the other hand, a lowering of pHto below 7.0 leads to shrinkage of the cells anddiminution of activity.

In pathological states, changes in reaction ofthe exudate are not necessarily correlated withalteration in the pH of the intercellular tissuefluids, and consequently no loss of activity maybe observed. It is possible for the secretions inthe epithelial surface to penetrate and to affect thecells; penetration of vegetable acids such as lacticand formic have been shown by Gray to producea depressing effect, while mineral acids have littleaction, owing to lack of passage into the cells.But the reaction of the tissue fluids is subject

to fluctuation; with an increase of the alkalireserve or with increased excretion of carbondioxide from the nasal epithelium, there may bea corresponding rise towards the alkaline side, withconsequent changes in ciliary activity. The ques-tion will be returned to later.OSMOTIC PRESSURE. The influence of changes

in this respect has already been covered, more orJess, in connexion with the supply of ions andthe concentration of hydrogen ions. Osmotic pres-sure must be so balanced as not to lead to oedemaor to dehydration, both of which impair the activityof epithelial cells. In experimental investigationsit is essential that the medium used should beisotonic, if functional activity is to be maintained.EFFECT OF GRAVITY.-Experiments show that

change of position has no appreciable effect onthe rate of ciliary streams. The question is one ofimportance, because it might be thought that thedrainage of the nose and sinuses would be moreefficiently carried out than that of the trachea andbronchi. From personal observation, this is notthe case, since gravity appears to have no effecton ciliary action. Thus in one experiment thetime taken to travel 1 cm. was 33 seconds in anupward direction, 26 seconds on the level, and34 seconds downwards.RATE OF PROGRESS.-In the nose the esti-

mated rate is 1 cm. in half a minute, or 2 cm. aminute (Proetz). In the bronchi progress is slower,at 0.25 cm. per minute (Proetz). Florey andothers (1932) found the rate to be 3.5 cm. in oneminute in the cat's trachea.DIRECTION OF STREAMS.-The pathways of

ciliary streams are fixed and unchangeable(Lucas, 1933). In the sinuses they are alldirected towards the ostium and therefore thecourse may be lengthy, since some of the streams

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must pass outwards across the floor, upwards onthe outer wall, and inwards across the roof beforereaching their -point of exit.

In the trachea there is a serpentine movementat the bifurcation, according to the observationsof Barclay and others (1937). This is to beexpected, since the streams from the two bronchimeet and coalesce. When the larynx is reached,the track is towards the posterior commissure,since there are no cilia on the vocal folds; thelatter regions, being covered with squamous epi-thelium, cannot propagate ciliary streams.

It is interesting to note the reported observationthat cilia always drive towards the point fromwhich they originated. If the lining of the maxil-lary sinus be removed, with regeneration of a newone from ingrowth and spreading in from theostium, the new streams will always be directedtowards the point of regeneration-that is, theostium.PROPAGATION OF IMPULSE.-An isolated epi-

thelial cell has four or five ciliary projections,which continue to beat if in a suitable medium.No nervous stimulation is at work, and apparentlynone is required, the rate of beat being an inher-ent attribute of the cell (Lucas, 1931). Propaga-tion through the cytoplasm from cell to cell issufficient to maintain an orderly sequence ofaction, as may be observed in a fragment of thegill of an oyster, in which a wave motion flowsalong the line of cilia. Nerve impulses may acti-vate ciliary movement, but they do not inhibit it;impulses pass by the parasympathetic portion ofthe autonomic system (Lucas, 1935).POWERS OF RESISTANCE.-The recuperative

powers are considerable under changes of tem-perature or under experiments with various drugs.Unless killed by excessive heat or by powerfulagents, such as cocaine of 10 per cent strength, arestoration of favourable conditions is followedby renewal of ciliary action. More will be saidlater on this point.REGENERATION.-It has been noted by Knowlton

and McGregor (1928), Gorham and Bacher (1930),and Hilding (1933) that ciliary epithelium mayregenerate, both experimentally in animals andafter operation in man, when the lining of a sinushas been removed. Regrowth must not, however,be relied upon, particularly if scar tissue forms inthe submucous layers (Hilding, 1932). Operationsfor removal of adenoids are naturally associatedwith denudation of a considerable area of the-naso-pharyngeal vault, but if performed withoutundue injury to the underlying aponeurosis,

replacement may be expected. But if roughcurettage has been performed scar tissue may beproduced, with consequent prevention of ciliaryregeneration; in such a case debris and bacteria,carried back from the nose and sinuses, may stag-nate in the naso-pharynx and lead to droplet infec-tion of the tracheo-bronchial tree.

In cases of acute rhinitis, shedding of the surfacemucosa may occur, followed, according to reports,by regeneration in a few hours under favourableconditions. Tissue culture of ciliated epitheliumhas demonstrated the outgrowth of cells with motileprojections (Lucas, 1933; Proetz and Pfingsten,1939).

FORCE EXERTED.-The strength of ciliary actionis very considerable, as may be observed by placingsome pieces of thick paper in the roof of themouth of a frog. In experiments with excisedpieces of epithelium, viewed on edge, the propuil-sion of blood corpuscles, used as indicators, isvery striking.

Hilding (1944) has measured the changes of pres-sure produced during the expulsion of a plug ofmucus from the trachea of a hen, and has foundit reduced to 40 mm. of water. He concludes thatsuch an action may play a part in deflation of thelungs and may be instrumental to a certain degreein producing the changes known to occur afterplugging of a bronchus in man. Massive collapsemay follow, even if not occurring before the plug-ging, especially after operations in the upperabdomen.Experimental observations show that cilia may

continue to wave without creating a marked pro-pulsive effect, owing to a decrease of amplitude ofthe stroke.

CONDITIONS PRODUCING DISORDERED ACTIONDRYING.-At the beginning of a cold in the

nose, probably through the action of the causa-tive virus, areas of mucosa, usually far back inthe fossa or on the upper surface of the softpalate, become dry. When this occurs ciliaryaction ceases at the margin of the dry patch; anybacteria carried back are left to stagnate and tomultiply. The mechanical action of the ciliarystreams is interrupted, and no longer are patho-genic organisms conveyed to the naso-pharynx,to be removed thence by peristaltic contraction ofthe superior constrictor, followed by a swallowingmovement travelling down the pharynx to theoesophagus. Furthermore, the absence of mucusremoves the protective action of lysozymes,-described by Fleming (1928); the inhibitory or

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bactericidal action of the secretions from the nose

and sinuses-and the tears from the eyes-is no

longer available to check the growth of the second-arily invading organisms. Drying is also causedby residence in overheated and undermoistenedrooms, when air-conditioning is inefficient; itappears also in the dry atmosphere of WesternAustralia and in the high altitudes of the Hima-layas. Atropine may do harm by reducing thequantity of secretions in the nose and tracheo-bronchial tree if given in an amount greater thanrequired to counteract the stimulating effect ofsuch an anaesthetic as ether. Atrophy of the nasalmucous membrane is accompanied by reductionin the amount of secretion and transudate, withconsequent infection.- Desiccating agents such as

chemical corrosives and caustics, the galvano-cautery, or diathermy, dry the surface but may

also destroy the cilia and produce scar tissue whichprevents regeneration.SWELLING OF EPITHELIUM.-It is found experi-

mentally that an excessive rise of the pH is accom-

panied by swelling of the epithelial cells, with finalcessation of action. Excess of one ion and theabsence of others may produce a similar effect;sodium tends to lead to swelling, and potassiumand calcium to shrinkage, all with disturbance ofciliary movement.

MECHANICAL OBSTRUCTION.-Blockage of thenasal fossae or of the ostium of a sinus by inflam-matory or allergic swelling or other cause inter-rupts ciliary action; similar changes may occur

in an inflamed bronchus or in one plugged by aninhaled.foreign body or by a plug of viscid mucus.

ITERRUPTION OF STREAM.-The presence of a

small foreign body in a bron_hus, even of insuffi-cient size to cause plugging, may encourage theappearance of granulations; these have no ciliaon their surface, and the ciliary stream is therebyinterrupted and secretions pile up on the distalside. This may occur in cases of bronchial orlung abscess.A drop of chloroform condensing in the trachea

may inhibit a band of cilia, thus interrupting thestreams completely and possibly permanently.As mentioned above, destruction of part of the

ciliary chain by coagulation, effected by the gal-vano-cautery or by surgical diathermy, is anothermeans of upsetting the mechanism. Similarly,removal of the epithelium at operation may havethe same effect; this may occur as the result ofremoval of adenoids. When the lymphoid massis shaved off, the covering epithelium must of neces-sity be removed; regeneration may be complete

and effective unless there has been damage to theunderlying aponeurosis or muscles. In the lattercase the formation of scar tissue is likely to preventthe regrowth of cilia. Operations on the sinusesshould be designed to interfere as little as possiblewith ciliary action ; the making of high and narrowopenings into the maxillary or sphenoid sinusesis therefore preferable to the creation of longwindows (Proetz).EFFECT OF DRUGS.-Apart from the actual des-

truction by such an agent as liquid chloroform,there are frequent occasions on which the incor-rect use of medicaments has a harmful effect(Negus, 1934).

Cocaine in concentrated solution inhibits cilia;2.5 per cent solution is almost harmless if appliedfor short periods, but 10 per cent causes cessa-tion of action, while stronger concentrations aresaid to be destructive. This observation is, how-ever, open to doubt, since patients to whose nasalmucosa 25 per cent paste, or cocaine mud, hasbeen applied do not seem to suffer eventual badeffects. Drying agents like atropine, in excess,are harmful, in that they remove the blanket ofmucus without which cilia cannot function; inoperations on the larynx, in particular, this drugshould not be abused, for fear of subsequent infec-tion of the inefficiently protected tracheo-bronchialtree. Ephedrine in half or three-quarter per centstrength has no direct ill effect, unless it dries thesccretion overmuch. Thymol is harmful, and soare most antiseptics except those of the silvergroup, such as argyrol and protargol in 2.5 or 5per cent strength. Not only may there be adeleterious effect by chemical action but also oneof a direct physical nature. Thus glycerine instrength makes the blanket of mucus too viscid,while oils, although not mixing with the waterymedium, have an entangling and impeding effect.What is spoken of as physiological saline solu-

tion is sometimes found in practice to be anythingbut beneficial if nasal douching is employed, sincethere is not only washing away of the blanket ofmucus, if the liquid is used too freely, but also aninhibitory effect, probably due in the main to desio-cation; the addition of borax or phenol to col-lunaria does nothing to obviate these objections;but, if used -judiciously, isotonic solutions madeup with sodium chloride are useful and harmlessif used in sprays.CHANGES IN REACTION OF MEDIuM.-The neces-

sity for the supply of a variety of ions in correctproportion has already been referred to, but inaddition there must be an accurate concentrationof hydrogen ions; this' means, of course, a reac-

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tion of the right order. This observation refers tothe epithelial cells and tissue fluids rather than tothe superficial secretions. Examinations of the pHof the tissue fluids and the secretions have beenmade by many investigators and by variousmethods, with varying results, as already described.In point of fact, the reaction of the medium onthe surface of the epithelium has no great effect onthe activity of cilia. Experiments show that ciliawork actively in a medium just below the neutralpoint, and even at as low a level as 6.5. On theother hand, a rise of pH to 8.0 or 8.5 is still asso-ciated with active ciliary action; but such a riseoccurs in the early mucoid stages of acute rhinitis,with a lowering of resistance to bacteria (Hilding,1934). In the later stages of suppuration in thenose or sinuses the reaction drops to below theneutral point, even to pH 5.86, according toBuhrmester (1933). Ciliary action may continuein an infected sinus (Proetz, 1933).

In life extreme variations do not occur, butsmall changes due to alterations in the alkalinereserve, or in the excretion of carbon dioxide,may affect the action of cilia. Ltischer (1930)has shown that the alkaline reserve is loweredwhere there is nasal obstruction; no doubt thediminished excretion of carbon dioxide accountsfor this change. In allergic states the pH rises,but infections are not usual; it may be concludedfrom this that ciliary action is not deleteriouslyaffected (Kreewinsch, 1932). The production oflactic acid by glycophilic bacteria has been referredto, with some possible effect on the epithelial cells.Vegetable acids such as lactic acid and formic acidpenetrate cell walls more readily than mineralacids such as hydrochloric; their effect on cellactivity may therefore be felt.

RELATIONSHIP BETWEEN UPPER AND LOWER AIRPASSAGES

Many particles of dust and many bacteria areprevented by the nose from entering the lower airpassages, provided, of course, that nasal respira-tion is maintained. Breathing through the mouthowing to nasal obstruction, or keeping the mouthopen when talking, naturally allows unfiltered airto enter the tracheo-bronchial tree. But if inspira-tion is effected through the nose, there is a con-siderable degree of filtering. This depends firston the presence of vibrissae in the nasal vestibule,secondly on the entangling influence of slightlyviscid nasal mucus, and thirdly, as Proetz hasdescribed, on surface attraction of particles bystatic charges. The secretions, with their con-tained debris, are dumped in the naso-pharynx,

to be removed by the swallowing mechanism. Buteven so, many bacteria must be carried down withthe inspired air during nasal respiration, and moreduring mouth-breathing. The ejection of thesefrom the bronchi and trachea is carried out by thelocal ciliary streams. And in cases of laryngec-tomy, when the trachea opens directly on the frontof the neck, the lower passages are able to remainin a state of health by virtue of their own defences.The ciliary mechanism of the nose is of assis-

tance in protecting the lungs, but alone it is notsufficient and must be supplemented by the defencesof the tracheo-bronchial tree. Furthermore, itmay be added that when the nasal or naso-pharyn-geal mechanism is deranged, the nose may becomea danger instead of a protection to the lungs.

CONCLUSIONSTo preserve ciliary action, and to assist its highly

important function of resisting infection, it is neces-sary to be acquainted with all the factors outlinedabove, and to take such measures in the preventionand treatment of disease as appear of assistanceto physiological processes. Thus the blanket ofmucus must not be washed away by nasal douches,nor must it be made too viscid by concentratedglycerine, nor too liquid by excessive use of potas-sium iodide. The secretions must not be dried byhypertonic solutions, by excessive use of amphet-amine or atropine, or by residence in an ineffi-ciently conditioned building. Secretions must notbe allowed to accumulate in a sinus or bronchus;they must be remov,ed, if excessive, by washingout or aspiration. No drugs must be employed,except for brief periods, which have a toxic effecton the mucosa; cocaine, thymol, and most power-ful antiseptics are in this category.

Obstruction to ciliary streams must be cleared,whether a plug of coagulated muco-pus in theostium of the maxillary sinus, a foreign body, ora mass of new growth in a bronchus; similarly,a septal deviation may need correction.

If an operation is performed in an area coveredby ciliated epithelium, every care must be takento avoid damage of a permanent nature. Thus,adenoids must be removed in such a way as toavoid scar-tissue formation- and to allow of regen-eration; in a sinus the opening must not be over-wide, nor should the mucosa be removed if cap-able of recovering and of once again serving itsphysiological functions, nor must cauterization beapplied to wide areas for fear of scarring.The reaction of the secretions must be regu-

lated where possible to facilitate free action; apH just above neutral appears best, and for this

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V. E. NEGUS

reason spray solutions are made slightly alkaline.The alkali reserve of the body may require cor-rection on occasion.

If all these points are kept in mind, and if ciliaryaction maintains its efficiency, then there will beno penetration of the mucosa by bacteria and nostrain will be thrown on the leucocytic second lineof defence.

REFERENCESBarclay, A. E., Franklin, K. J., and Macbeth, R. G. (1937).

J. Physiol., 90, 347.Buhrmester, Catherine C. (1933). Ann. Otol. etc., St

Louis, 42, 1041.Fabricant, N. D. (1941). Arch. Otolaryng., Chicago, 34,

150.Fleming, A. (1928). J. Laryng., 43, 385.Florey, H., Carleton, H. M., and Wells, A. Q. (1932).

Brit. J. exp. Path., 13, 269.Frenckner, P., and Richtner, N. G. (1940). Acta oto-

laryng., Stockh., 28, 215.Gorham, C. B., and Bacher, J. A. (1930). Arch. Oto-

laryng., Chicago., 11, 763.Gray, J. (1920). Quart. J. micr. Sci., 64, 345.Gray, J. (1921-2). Proc. R. Soc. B, 93, 104; 93, 22.Gray, J. (1928). "Ciliary Movement." London: Mac-

millan and Co.Hellmann, K. (1926). Z. Laryngol. Rhinol., 15, 1.Hilding, A. (1932). Arch. Otolaryng., Chicago, 15, 92.Hilding, A. (1933). Arch. Otolaryng., Chicago, 17, 760.Hilding, A. (1934). Ann. Otol,, etc., St Louis, 43, 47.Hilding, A. C. (1944). Anesthesiology, 5, 225.Hill, L. (1928). Lancet, 2, 802.Knowlton, C. D., and McGregor, G. W. (1928). Arch.

Otolaryng., Chicago, 8, 647.Kreewinsch, P. (1932). Acta oto-laryng., Stockh., 17,48.

Lillie, R. S. (1906-7). Amer. J. Physiol., 17, 345;Linton, C. S. (1933). Ann. Otol., etc., St Louis, 42, 64.Lucas, A. M. (1931a). J. Morph. Physiol., 51, 147.Lucas, A. M. (1931b). Trans. Amer. laryng. rhin. otol.

Soc., 37,172.Lucas, A. M. (1933). Proc. Soc. exp. Biol., N.Y., 30,

501.Lucas, A. M. (1933). Arch. Otolaryng., Chicago, 18, 516.Lucas, A. M. (1935). Amer. J. Physiol., 112, 468.Lucas, A. M., and Douglas, L. C. (1933-4). Proc. Soc.

exp. Biol., N.Y., 31, 320.Lucas, A. M., and Douglas, L. C. (1934). Arch. Oto-

laryng., Chicago, 20, 518.Luscher, E. (1930). Acta oto-laryng., Stockh., 14, 90.McGregor, G. (1931). Arch. Otolaryng., Chicago, 14, 309.Mittermaier, R. (1930a). Arch. Ohren-Nasen- u. Kehl-

kopfheilk., 126, 390.Mittermaier, R. (1930b). Z. Laryng. Rhin. Otol., 19, 390.Negus, V. E. (1934). J. Laryng., 49, 571.Proetz, A. W. (1929). Ann. Otol., etc., St Louis, 38. 963.Proetz, A. W. (1932a). Ann. Otol., etc., St Louis, 41, 125.Proetz,A. W. (1932b). Ann. Otol., etc., St Louis, 41, 1117.Proetz, A. W, (1933). Ann. Otol., etc., St Louis, 42, 778.Proetz, A. W. (1934). J. Laryng., 49, 557.Proetz, A. W. (1941). "Applied Physiology of the Nose."

Annals Publishing Co. St. Louis.Proetz, A. W. (1944). Arch. Otolaryng., Chicago, 39,514.Proetz, A. W., and Pfingsten, M. (1939). Arch. Oto-

laryng., Chicago, 29, 252.Purkinje, J. E., and Valentin, G. (1834). Arch. Anat.

Physiol., Lpz., p. 391.Sharpey, W. (1830). Edinb. med. surg. J., 34, 113.Sharpey, W. (1835a). Edinb. new philo. J., 19, 114.Sharpey, W. (1835b). Article on cilia in Todd, R. B.,

"Cyclopaedia ofAnatomy and Physiology." London.Thomson, St. Clair, and Hewlett, R. T. (1895). Med.-

chir. Trans., 78, 239.Tweedie, A. R. (1934). J. Laryng., 49, 586.Yates, A. Lowndes (1924). J. Laryng., 39, 554.

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