IVAN PETRO V ICH PAVLOV

1849-1936

W it h the death of I v a n P e t r o v ic h P a v l o v on 27 February, 1936, in his 86th year, there passed away one of the greatest physiologists of the last and the present century. Pavlov was possibly also the most popular and the best known man in the physiological world. The immense prestige which he had and the esteem in which he was held by his contemporaries can only partly be explained by his outstanding scientific achievements; to a large extent they were also due to his remarkably attractive and arrest­ing personality. His impulsive, straightforward, on the whole rather simple, joyous, and kind attitude to everybody around him evoked a feeling of warm affection and admiration in all who knew him. Coming from far distant Russia, during his long and active life—Pavlov was born on 27 September, 1849—he reached a position in Science which was unique, almost legendary. In order to understand Pavlov he must be described both as a scientist and as a man.

Pavlov, the eldest son of a poor priest, was born in Central Russia in the rather out-of-the-way district town of Ryazan. The life of the provincial clergy was at that time an extremely difficult one. In fact, it hardly differed from that of the peasants. The clergyman had to work his own land and had practically no other source of income beside the food which he could raise himself. It was entirely due to the lifelong perseverance of Pavlov’s grandfather, a simple servant in a village church, that Pavlov’s parents could at all move to and settle down in a town. Again by sheer perseverance, fighting against heavy odds, but with unassailable moral standards and a highly developed sense of duty, Pavlov’s father gradually advanced in his position and finally obtained one of the best parishes of Ryazan. The tenacity and perseverance, the atmosphere of hard physical labour, together with the intellectual superiority of the clergyman’s family, had a strong influence in the moulding of Pavlov’s character.

Strong in health, exuberant in energy, Pavlov’s chief characteristics were an extraordinary sense of duty and a tenacity in everything that he undertook. His expressions and opinions about things and people were always definite and seldom changed. On the whole, he was frequently intolerant and always extremely exacting in relation to others and even more so to himself. He had the greatest contempt for anything

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bordering on slackness or negligence and did not spare the feelings of people in telling them so ; but none of his pupils and co-workers ever could take offence because of the example which Pavlov himself set them by his great sincerity, and because he never bore a grudge against anybody for long. He would be in a blazing fury to-day, to-morrow he would forget all about it and would be genuinely hurt if one reminded him of it. “ A good flare-up never harmed honest work ” he would say, using a Russian proverb, and proceed as if nothing had happened. Possibly those who were nearest to him and whom he himself really valued had to bear with this impulsiveness most : he would very likely completely disregard the existence of those whom he did not appreciate. It was, however, only the minor happenings that he treated in such a light­hearted and boyishly unrestrained m anner; in questions that really mattered he exhibited the family trait and hardly ever changed his point of view or opinion once it had been made.

I shall never forget the following incident. During a demonstration to the students one of his nearest co-workers, a man to whom he was personally deeply attached, placed his head—he had rather abundant and curly hair—right over the operation field. The experiment went well. Pavlov as usual waving his hands with a radiant and yet con­centrated expression on his face, gave explanations to the audience, but the students could not see. A low dissatisfied murmur drew Pavlov’s attention to the offending head. Without a moment’s hesitation, with both hands the head of the short-sighted assistant was rudely pushed aw ay; he lost his balance and would have fallen had somebody not caught him. Pavlov was furious—it was, of course, all the assistant’s fault. At first Pavlov went on with his explanations as if nothing had happened, then suddenly rushed out of the lecture theatre and with his usual impulsiveness smoothed out the matter. “ Of course it is all your fault, what else could I do ? I had to push you away, but there is no need to take it to heart—just forget it and come and help me to go on with the experiment ” . Whoever worked with Pavlov must know of many similar incidents. He would never quite admit his own fault in these minor outbursts, but he would feel extremely miserable if offence were taken at his impulsive reactions. He was perfectly sure that anybody else would act under the circumstances in exactly the same way.

The first years of Pavlov’s life seem to have proceeded entirely in a sphere of purely physical development. As a boy he took an enthusiastic and frequently leading part in the primitive games and skirmishes of the village children. Again, while others seemed to be playing anyhow, just for fun, Pavlov showed even in games his usual tenacity. He

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constantly tried to improve himself in whatever he tackled. Left- handed like his father, by persistent practice he succeeded in becoming ambidextrous. It was a hard task to assist Pavlov during an operation. One never knew which hand he would use next. He made sutures with the right and the left hand with such rapidity that two men were required to supply him with threaded needles. On several occasions I have been able to time him during various minor and major operations. A tran­section of the spinal cord in the upper cervical region took him seven seconds. I saw him tie a cannula into the pancreatic duct in twenty- five seconds; an innervated gastric pouch, aseptically performed, was once made by him in forty-five minutes. Anyone familiar with these operations will appreciate the enormous skill needed for such perform­ances.

The delight in physical achievement and exercise remained with Pavlov to the end of his life. Up to his latest years he would frequently organize various physical competitions and even play in the yard of his Institute some vigorous game. A photograph exists showing Pavlov at the age of 75, with a number of his colleagues, armed with Russian baseball clubs. He organized a gymnastic society amongst the medical staff of his Institute. Such was his enthusiasm that even the rather sedate temperament of the average Russian intellectual was overcome. Pavlov always used to say that he appreciated the feeling of “ physical satisfac­tion ” more acutely than that of “ mental satisfaction ”—“ muscular joy ” he would call it.

When seven years old Pavlov began lessons. He did not like them. He would constantly manage to escape to dig next his father in their vegetable garden or to do some carpentry or wood-turning. Between the age of eight and ten, young Pavlov’s health became rather indifferent as a result of a bad fall from a high fence. His regular studies had to be postponed. He entered an elementary theological seminary at the age of eleven and was for a long time physically handicapped. Here again the persistence of Pavlov helped him to overcome this handicap. He set himself the aim of becoming as strong as before, and while his brothers and friends indulged in various pleasures Pavlov persistently trained himself by various exercises. He even succeeded in persuading his father to rig up in his garden a special apparatus for drill.

Pavlov did not distinguish himself in any way during his school career in the preliminary and then secondary theological seminary. He liked taking part in debates and discussions upon various problems. When­ever Pavlov was present the discussion at once became extremely stormy ; his enthusiasm and logical thinking always carried the audience. Tenacity

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was again his main trait. I remember, when I was a second year student, that somehow or other a discussion arose in Pavlov’s laboratory in respect of the comparative values of different fine arts, as to which of them is a sign of greater superiority of racial development. Pavlov was for painting and sculpture, I and some others were for music. No one would give way. We dug in encyclopaedias and books to find support for our respective points of view ; each side was persistent to the extreme. How persistent can be seen from the fact that the discussion started in Russia in 1913 but reached its height in 1927 while Pavlov was staying in Cambridge.

In 1870, Pavlov entered the Faculty of Science of the University of St. Petersburg. During the first years at the University he did not show any special brilliance as a scholar, and only in the third year of his studies, chiefly due’ to the influence’ of Zion (Cyon), who was Professor of Physiology, did Pavlov definitely settle on this subject and took it up with his usual unbounded enthusiasm. Professor Zion, the discoverer of the depressor nerve, was an extremely brilliant lecturer and skilful experi­menter. His demonstrations fascinated Pavlov who resolved to test his hands in experiments himself. The first research ever made by Pavlov was suggested to him by Zion over sixty years ago; the problem was to study the secretory innervation of the pancreatic gland. This investigation, which has never been published, was awarded the Gold Medal of the University. Pavlov was taken by research in earnest; from now on he considered it above everything in life. He showed his enthusiasm from the very beginning by sacrificing one whole year of his University studies in order to be able to complete the research given to him by Zion. In 1875, Zion was elected to the Chair of Physiology at the Medical Academy and offered the newly graduated Pavlov the post of assistant, which he gladly accepted. While performing his new duties Pavlov registered as a medical student in order to obtain a medical qualification in addition to a science degree.

An unfortunate event occurred at that time. The election of Zion to the Medical Academy, which was made on the recommendation of such men as Ludwig, Pfliiger, Helmholtz, and Claude Bernard, was revoked by the Government, the reason being that Zion was of Jewish extraction. The incident with Zion was coupled with considerable and rather degrading intrigues against him amongst students as well as teachers. Zion, one of the greatest of Russian physiologists, had to leave Russia for good. Pavlov resigned forthwith and declined to be an assis­tant to Zion’s successor, a pompous scientific nonentity. It was typical of Pavlov to have taken such an uncompromising attitude from which no material interest could move him. In later years, when lecturing on

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the depressor nerve, Pavlov would never fail to describe to the students details of Zion’s dismissal. He would pour furious scorn on administrative interference with matters of science. On the whole intolerant in minor matters of everyday life, Pavlov was extremely broad-minded in matters of higher importance.

After some time Pavlov succeeded in obtaining a post of Assistant at the Veterinary Institute which he held for two years. In the summer of 1877 he collected sufficient funds to visit the famous Physiological Laboratory of Heidenhain in Germany. Heidenhain worked at that time almost entirely on digestive problems. First directed into these lines of investigation by Zion and now by Heidenhain, half of Pavlov’s life became devoted to the study of digestion.

It is of interest to mention that already early in Pavlov’s career “ train­ing ” as a method of scientific investigation began to interest him, and was used by him in studying various digestive and circulatory problems. Pavlov first started to train his animals as early as 1878 for the purpose of measuring the normal blood pressure. Wishing to know the effect which digestion and various other influences had upon the normal blood pressure, Pavlov trained his dogs to stand perfectly quiet with a cannula inserted into one of the leg arteries. The whole procedure was carried out without anaesthesia. The animals behaved normally and did not exhibit any sign of discomfort or pain. Later, of course, training of the experimental animals assumed the greatest importance in connexion with Pavlov’s work on conditioned reflexes. In fact, the quality of the scientific worker was, to some extent, judged in Pavlov’s laboratories by the behaviour of his dogs during the experiment. I remember an incident when a newly arrived investigator complained to Pavlov that his dogs would not keep quiet during some delicate experiments on conditioned reflexes. Pavlov called some of us to his room and exposed the doctor as a social danger, prophesied all sorts of misfortunes in his life, and told him that he would have to leave the laboratory unless his dogs behaved. The training consisted chiefly in a serious, matter-of-fact attitude towards the dogs during the work. The animals were never beaten, nor bribed by petty kindness.

Pavlov obtained his medical qualification in 1879 with a delay of one year on account of the Russo-Turkish war. His research work and general abilities were greatly appreciated. He was awarded a Gold Medal of the Academy and a research Scholarship. Being true to his principles, he still declined, after the incident with Zion, to join the Physiological Labora­tory in the Medical Academy; instead, he was placed in charge of an experimental laboratory, which an enlightened Professor of Medicine in

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the Academy, S. P. Botkin, had created next to his clinic. Such a laboratory was considered at that time an almost unheard-of novelty. The prob­lems to be worked upon were usually selected by Botkin; Pavlov had to see to their execution. Young doctors from the clinic would come and place themselves under Pavlov’s direction to work upon questions which frequently were of no interest to Pavlov himself. This naturally took a lot of his time and diverted his attention from his own work. It had, however, the compensation that it developed in Pavlov a talent for organization of research. Pavlov could conduct a large number of investigations at the same time with the greatest ease. He could in a moment switch off his mind from one problem to another. He would remember every detail of previous experiments, and in every case without the slightest confusion would pick up the threads of reasoning exactly where he had left them. In Botkin’s laboratory he had to deal possibly with not more than five or six scientific problems at the same time, but at the height of his career during his work on conditioned reflexes he had some­times over sixty people at work, everyone on a different problem. He directed three laboratories, and so far as I remember Pavlov was never at a loss as regards even the slightest details of each individual problem.

Pavlov married in 1881. His wife came also from the family of a priest. Three years later he obtained the M.D. degree and the title of Privat Dozent of the Academy. He was also given two years’ leave for scientific work abroad which he spent in the laboratories of Heidenhain and Ludwig. These two great physiologists must be considered as his immediate teachers. In discussing them Pavlov would frequently say that he took Heidenhain as an example of passionate devotion and enthusiasm to science and Ludwig as an example of restrained precision in observation—two main attributes which Pavlov considered as essential for a successful study of nature.

On his return from abroad to his old post in the Medical Academy, Pavlov gave himself up with complete abandonment to scientific research. Nothing could deviate him from his work; in fact, he even transformed a part of his modest apartment into a laboratory. He took some of his operated animals home, where together with his wife he would nurse them day and night. At first, circulation as a result of Ludwig’s influence and then more and more the physiology of digestion as a result of the early influence of Zion, and later of Heidenhain, took up his attention. In 1888 Pavlov discovered the secretory nerves of the pancreas. In the following year he described his famous experiments with sham feeding and discovered the secretory nerves of the stomach; soon he started his observations on chronically operated animals and applied the fistula

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Ivan Petrovich Pavlov 1

method to the investigation of the entire gastro-intestinal tract. Gradu­ally his work on digestion spread out broader and deeper and he con­tinued to work on it with growing success until about 1905.

Although already extremely successful as an investigator, Pavlov had several disappointments in his early professional career. He applied for the Chair of Physiology at the University of St. Petersburg and was not elected, the successful candidate being N. E. Wedensky. Soon after, he was offered the Chair of Physiology in Tomsk, Siberia ; the election was not, however, ratified by the Government. Finally, he was almost simultaneously elected to the Chair of Pharmacology at the same University of Tomsk, to a Chair at the University of Warsaw and to a Chair of Pharmacology at his own Medical Academy. He accepted the latter and was appointed. He held this post for almost five years until 1895, when he was finally transferred to the Chair of Physiology. In 1889, at the instigation and to a large extent at the cost of one of the Royal Princes, an Institute of Experimental Medicine was built. It was modelled after the Institut Pasteur of Paris. Amongst its several labora­tories was one especially devoted to Physiology. My father, who was appointed as its first Director, told me that while he was designing and organizing the Institute the enthusiasm of Pavlov was unlimited. Pavlov did not care what sort of accommodation he got except that everything should be done with the utmost speed and that the laboratory should have a first-class aseptic department. While new laboratories were built for other subjects, Physiology had to be placed in an old building. Pavlov did not mind this at all so long as he could start work at once ; in fact, he was always sceptical about the modern tendency to build palaces for scientific laboratories. “ Gilded uniforms never won a battle,” he would say. He considered that a certain degree of dis­comfort is good for a fertile mind and that a shortage in apparatus and material trains resourcefulness. In 1891 Pavlov took charge of the new department. This gave him at last considerable facilities for research, and also improved the purely material side of his life.

During his medical studies as a student Pavlov had always been more interested in Surgery than in Medicine ; this interest left a deep im­pression in all his subsequent studies. It was the realization of the great importance that Surgery was designed to play in experimental research which made Pavlov insist that a proper operation theatre and hospital should be built in the Physiological Institute. I believe it was the first attempt to do so. To-day there is no proper Physiological Institute without some arrangement for aseptic surgery. Generally speaking, it was always the immediate, the mechanical, the perfectly obvious

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which appealed to Pavlov most. For instance, Pavlov never knew and rather mistrusted chemistry to the end of his life. This can be seen thoughout his scientific career. The Eck’s fistula, consisting in the isolation of the liver from the portal circulation, interested him chiefly as a surgical feat. He discovered the curious and not yet fully understood effect which meat produces in these animals, but the investigation of the chemical changes following this operation was left to others. He was not really interested. In relation to the Eck fistula, Pavlov told me the following incident : Dr. V. Eck, a young surgeon and a close friend of Pavlov, constantly used to joke about the incompetence of physiologists of that day and gave as an example the liver, the largest organ of the body, but of which nothing is known except that it produces bile and deposits glycogen and fat. Surgeons should really work in Physiology, teased Eck, and on a piece of paper he drew a sketch suggesting the operation which is now known as Eck’s fistula. I do not know whether Eck ever attempted to make this operation himself; if he did he was not successful and it is only due to the skill and persistence of Pavlov that the proper technique was developed. I t also shows the broad-minded­ness of Pavlov that he himself called the fistula by his friend’s name.

Hoping to discover the secretory nerves of the mammary glands, Pavlov quickly realized that such did not exist and that their secretion is controlled by hormones; he dropped the question at once. When Bayliss and Starling in 1902 demonstrated the secretin mechanism of pancreatic activity, Pavlov lost much of his interest in the pancreas. The first, the nervous phase of gastric secretion which he discovered early in his work, always fascinated him, the second, the chemical phase dis­covered by him somewhat later, rather puzzled, I could almost say, annoyed him.

It is remarkable that Pavlov, a man of such tremendous vitality and impulsiveness, was nevertheless extraordinarily regular in the distribution of his time. Punctual to the minute—he was never known to be late for a lecture—his operations, experiments, and all his laboratory work was carried on exactly to time. A fury of indignation was poured on the slacker, no excuse would be accepted* Regular in his work he was as regular outside it. Exactly at a definite moment he would disappear to his private room where he would brew tea for himself in a chemical flask. Punctually every day he would end his labour, more frequently than not walk at a sharp pace a couple of miles to his house, dine with his family and after infinite glasses of tea he would rest for an hour or two, waking up later in the evening to work alone, undisturbed in his study. To everything that he did he gave himself completely without

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reservation. In work, in leisure, in passing judgm ent upon people and their achievements, he never had a middle course or an intermediate shade of opinion.

During the summer holidays, which up to the revolutionary period he spent in Esthonia, Pavlov would have nothing to do with Physiology. I remember one occasion when as a young man driven to desperation by some intricate experiments on conditioned reflexes I decided to go and see Pavlov in the country. I stayed with him for two days. Pavlov was glad to see me. He showed me his flowers, made me dig in the garden and carry water, made me weigh cucumbers which were artificially supplied by him with various sugars and grown upon different manures. We bathed in the sea and talked about everything on earth, but I was never given the chance even to mention my problem. Everything with Pavlov was complete, full out in work, full out in rest. He would frequently say that a perfect machine should be able to reach within the shortest time a state of maximal activity as well as an immediate and complete state of inhibition or rest. The stronger the engine the stronger and more immediate should be the brakes. This peculiarity was in him paramount. With the greatest facility he could deliberately and suddenly change from one line of thinking or from one activity to another. He could deliberately shut his eyes to disturbing and unpleasant factors although a moment ago they might have gripped him very deeply. He never forgot them and kept on returning to them until he would finally conquer or solve them, but meanwhile he could set his brain free and devote himself to other interests. These interests outside his work were extremely varied. He was always on the look-out for joy and he derived it from hundreds of sources. Books, especially historical books, garden­ing, collecting almost anything from butterflies and stamps to good paintings, could at any time completely absorb his attention. This spiritual as well as physical freshness he kept to the end ; it is enough to mention that in 1918, at the age of 69, during the time of the revolutionary period when food was so scarce, Pavlov would regularly ride for several miles on his bicycle to work in a vegetable garden. As regards his instinct for collecting, Pavlov used to say that it should be strongly developed in every scientific worker. After all, what else is our work but a constant col­lecting of new facts and the systematizing of old ones ? During the summer vacation he was simply in need of satisfying this instinct by other means, and as in everything else he would do so with enthusiasm. It was curious to watch old Pavlov creep on tip-toe towards some butterfly, whispering endearing terms and imploring it not to move until he got it. He was genuinely miserable if he failed and for days he would tell every­body about his bad luck.

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The frankness of Pavlov naturally created for him various difficulties in his relations with administrative authorities. Many of these tried to hinder his material advancement in the Medical Academy, and his laboratory was for a long time treated as rather an unimportant section. In Russia, in order to obtain the M.D. degree, a candidate had to submit a thesis prepared in a recognized laboratory in addition to passing examinations in all the subjects of the medical curriculum. Due to the strained relations existing at that time between Pavlov and the adminis­tration of the Medical Academy, he had at first only very few such candidates. Later, conditions improved so that through these candidates Pavlov found an outlet for his fertile mind. They were the hands who under the immediate supervision of the staff of Pavlov’s laboratories and directed by himself performed the spade work of research.

As head of a laboratory, Pavlov was always extremely stimulating. He knew how to raise the interest of his co-workers even when the work itself was tedious and dull. It should be remembered in this connexion that the preparatory stage in the work on conditioned reflexes sometimes extends over many months before the first experiment can be attempted. At the time when Pavlov was chiefly engaged in the study of digestion he would take an active part in the experiments himself. Most of the vivisection experiments were performed personally by him. In experi­ments on aseptically operated animals which were subjected to long periods of observation Pavlov would have his co-workers watch the animals, himself dropping into their rooms to see the results and to discuss future work. As a man who was permeated with an impatient desire to have quick results Pavlov simply could not bring himself to watch or carry on any procedure lasting a long time without any apparent results. He was patient enough to accumulate very gradually the results of observations made by his co-workers, but himself he needed action. Possibly this explains the curious fact that Pavlov, from whose laboratories several hundreds of publications on conditioned reflexes were made, never worked on conditioned reflexes himself. In fact, I believe that he never even attempted to establish a conditioned reflex in a dog.

In discussing the results of an experiment with his co-workers as well as during his lectures to the students Pavlov knew how to present most intricate facts in an extraordinarily lucid and interesting form. Whatever he discussed he would completely dominate the attention of the audience. His lectures did not sound like proper lectures at all, they were rather more like discussions about what he himself thought upon the subject. Pavlov very rarely made reference to physiological literature, partly on account of the fact that he was a bad linguist, partly because, having to a

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large extent himself created the subjects of the physiology of digestion and of conditioned reflexes, he had no need to refer to other literature than that which came out of his own laboratories. In his lectures to the students Pavlov would never attempt to cover the whole course of physio­logy. He was convinced that lectures should not aim so much at teaching the subject matter of science as at teaching the manner in which prob­lems of science should be approached, how one should think and analyse a physiological event. Therefore he considered it entirely sufficient to lecture to the students on digestion, circulation, and conditioned reflexes only. He did not lecture on any other parts of physiology, omitting them altogether or referring them to some of his assistants. Those subjects, however, which he did lecture upon he went into very deeply, discussing all their aspects and difficulties in detail. He frequently said that it did not matter whether the students memorized a great number of facts so long as they learnt from his lectures how to think. Once the interest is aroused, the acquisition of the knowledge of facts as such and the learning of the rest of physiology would be a simple matter and should be done by the student himself.

He never employed mathematics even in its elementary form. He frequently said that mathematics is all very well but it confuses clear thinking almost to the same extent as statistics ; besides, mathematically inclined physiologists usually glory in abstruse equations and figures chiefly because of an inability to express things in a simple way. Theo­retical interpretations in general had very little value for Pavlov; “ use facts and do not theorize ” was his constant saying.

Pavlov in his own discussions on research frequently expressed the opinion that the mind of an investigator must always strive to answer the two major questions of “ what ? ” and of “ how ? ” Jokingly he would even classify contemporary physiologists into “ what-minds ” and “ how-minds ” . The realization of this division, said Pavlov, helped him to become both and, in fact, he was as great in discovering new phenomena which he approached from the point of view of what happens when an organism is placed under definite strictly controlled conditions as he was when he would analyse the mechanism of a phenomenon and try to answer the question as to how it happens. This attitude helped him to realize that in every biological process, just as in every physical phenomenon, things may proceed quite differently depending on the conditions under which the observation is made. From his very early work the conditions of the experiments were meticulously controlled, registered, and tabulated. During experiments on conditioned reflexes, we sometimes had to record things which seemed to have no importance

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whatever, such as yawning or sneezing of animals, or a small noise reaching the experimental room. It seemed so futile, but a great number of dis­coveries were made as a result of the searching analysis to which all those apparently irrelevant details were subjected.

The number of his co-workers in the three laboratories under Pavlov’s direction rapidly increased. In 1907 the Physiological Laboratory of the St. Petersburg Academy of Science was also placed under him. At about that time his interest in digestion began to diminish, and all his energy became concentrated on conditioned reflexes. The group of workers increased still further, but most of them stayed with Pavlov only for a year or two in order to obtain their M.D. degree; few could be regarded as his proper pupils. Towards the end of his career he resigned the Professorship at the Medical Academy where he was replaced by L. A. Orbeli, Pavlov himself retaining the supervision of the other two laboratories.

Pavlov was an extremely bad correspondent, either he would not answer letters at all or would delay the answer for months. In fact, writing even of scientific communications had always been for him an unpleasant labour. His desk would be full of completed research work which would lie untouched for months and years. When he finally settled down to write a paper he would dig out his old records and notes and more frequently than not, after looking through them, become so dissatisfied that the whole problem had to be once more investigated. Even after completing a paper he never sent it to press at once, he always left it, as he would say, to mature. “ Many a hasty publication led to a downfall; let this one mature for a while ” .

In most cases before writing a paper Pavlov would give one or several lectures upon the subject and have them recorded in writing. In this way originated his famous books on the physiology of digestion and on conditioned reflexes, in addition to the collection of various single lectures on different subjects. In connexion with his book on conditioned reflexes, it took years of persuasion to make Pavlov write it. He started, I believe, late in 1917, and it needed an unfortunate accident to begin his work. One frosty morning I was walking towards the laboratory when I saw from far away an old man supporting himself on an iron fence. The man was obviously losing his balance; at first I just accelerated my pace to see what had happened. Approaching, I saw to my horror that it was Pavlov deathly pale and weak. Apparently he had slipped on the ice and hurt himself. With the help of a passing car I transported him to the laboratory where an impacted fracture of the neck of the femur was diagnosed. Pavlov’s reaction was typical. At first and most violently

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he cursed his ill luck and then suddenly he smiled and in a most engaging way said rather slyly, “ Do you know I ’ll trick my bad luck and I ’ll t|irn it to a real profit; at last I shall have time to write my book He did write it and left it to “ mature It went on maturing until 1926. In 1923, when Pavlov was in London, I remember a most violent conversation that I had with him on this subject. Only by violent means could one make any impression on Pavlov. I simply asked him whether he hoped to live for another half-century and as that was doubtful whom did he intend to write up the conditioned reflexes for him. Pavlov was taken aback and frankly admitted that it was his duty to publish a com­plete review of his work, but, he said, “ I am just in the midst of making most interesting observations and especially on myself. It is so amusing to watch myself growing old and to observe which faculty diminishes and disappears first. Old age has such a lot of advantages I feel that I have now acquired an extraordinary freedom in thinking, a great faculty of arriving rapidly at conclusions, making plans, discovering relation­ships, and analysing intricate experiments. My mind has become much freer than it ever was before. O f course, I know that this is all due to the fact that I am rapidly losing the faculty of self-criticism ; inhibition is so much more delicate a process than excitation; we see it every day in conditioned reflexes and now I am observing it on myself” .

Turning to the purely scientific achievements of Pavlov, his career is fairly sharply divided into three periods. In the first preliminary period he worked partly on digestion and partly on circulation. The second was devoted completely to the investigation of secretion of the digestive glands and to the action of the digestive juices. The third period spontaneously, within about two years, grew out of the second. Pavlov gradually left digestive work and concentrated on conditioned reflexes.

In order to appreciate the importance of Pavlov as a scientific worker, it must be clearly realized that he began his career at a time when the method of rigid scientific analysis as we know it at present hardly existed. Biological phenomena, especially those taking place in the higher mammals, were still approached with a sort of feeling of mystery; they were frequently regarded, if not quite as supernatural, as “ vital ” , as ready to work at any moment not quite in accord with the laws of physics and chemistry. Pavlov’s immediate teachers, Zion and Ludwig, were already fighting against such tendencies, but Heidenhain to the end of his days continued to consider physiological processes in a somewhat vitalistic light. Pavlov’s mind as far as science was con­cerned was entirely materialistic ; he never changed it during the whole of his long life. It is difficult, however, to say to what extent his personal

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existence was dominated by this materialistic tendency. In Soviet Russia Pavlov was represented as a leader of anti-religious ideas. This he certainly never was ; nevertheless, it would be hard to say whether he ever was what is commonly known as a religious man. It is unquestion­able that he had the greatest respect for religion as such. In this he remained true to his early theological education and to his family tradition. But on many#occasions, when he undoubtedly experienced a feeling of worship evoked by some religious occasion, he would suddenly start discussing religion as one of the most valuable social conditioned reflexes.

Almost all of Pavlov’s work on circulatory problems was performed within the first ten years of his scientific activity (1878-88). Partly still under the influence of Zion, but chiefly under that of Ludwig, Pavlov investigated the efferent nerves of the heart. By extremely skilful dis­section he succeeded in isolating the cardiac branches which cause, on stimulation, an augmentation of the strength of the heart beat from those which influence the heart rate. He also studied the effects of various drugs upon them. Pavlov designed and made the first heart-lung preparation in order to find the various influences which determine the output of blood by the heart. He discovered the pressor influence of the vagus nerve which he regarded as a corollary to the depressor influence discovered in Ludwig’s laboratory by Zion.

The circulation did not keep Pavlov’s attention for a long time. He always returned to digestive problems. In this he was influenced by Heidenhain, who already at that time extensively applied the fistula method to the study of the digestive tract. From about 1888 till 1906 over 130 scientific communications were published from Pavlov’s laboratories dealing with one or another aspect of secretion and diges­tion. The leading idea which guided his work on digestion was the same as in his circulatory research, namely, to study each function in relation to definite internal and external conditions and to determine the exact part played by each of these conditions while keeping the other conditions constant. Up to Pavlov’s time, the importance of such pre­cautions had not been properly realized ; functions were studied on isolated organs or in animals in extremely abnormal conditions owing to the action of various anaesthetics or as a result of pain. He realized the disturbing influence of these factors and painstakingly eliminated them in his research. Pavlov discovered the secretory nerves of the stomach and of the pancreas; he determined the exact relation between different kinds of food and the character and amount of every digestive juice. He performed his famous experiments on sham-feeding, investigated the

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Eck fistula, discovered the acid control of the pyloric sphincter, discovered and analysed the inhibitory action of fat on the secretion of gastric juice and on the movements of the stomach. He discovered the chemical nature of the second phase of gastric secretion, studied the secretion of bile and determined the factors which influence it. He investigated the movements of the gall bladder, described the local “ mechanical ” mechanism of intestinal secretion and discovered enterokinase ; he studied the activity of the digestive glands after the destruction of their nerve supply and under various other pathological conditions. He was the first to succeed in keeping animals alive for years after double cervical vagotomy. Among his operations, besides the Eck fistula, the most famous are that of gastro-oesophagostomy for the purpose of obtaining large quantities of pure gastric juice and that of the innervated gastric pouch, at present known as Pavlov’s pouch in contrast to the denervated pouch first made by Heidenhain.

Dr. Dolinsky in 1894 discovered in Pavlov’s laboratory the striking effect which injection of acid into the duodenum has in evoking secretion of pancreatic juice. Being primarily “ nerve-minded ” and having had a similar example in acids evoking salivary secretion when applied to the mouth, Pavlov was convinced that an identical mechanism underlay both secretions. Only in 1902 did the discovery of secretin by Bayliss and Starling give the correct interpretation to the action of acid on the pancreatic secretion. As soon as this discovery became known, Pavlov at once repeated the experiments which succeeded most definitely. Pavlov’s reaction was typical ; rather depressed, he quietly retired to his study. After some time he came out, he was again quite happy and said jokingly, “ Most certainly they are right, after all, we cannot hope to have the privilege of discovering all the new facts in digestion ” . The question was settled for him once and for all. He could never, however, under­stand why, while he so willingly accepted the discovery of Bayliss and Starling, the British physiologists would flatly deny his own discovery of the secretory pancreatic nerves. The universal acceptance of these was made only as late as 1913.

It would be useless hereto describe all that Pavlov did in the physiology of digestion; it is sufficient to say that digestive processes were only hazily understood before the advances made by Pavlov’s school. Most of the facts relating to digestion, as it is now known, either had their origin, or were established, in Pavlov’s laboratory. In 1897 a collected account of his work was brought out in German and in French. A little time later an English translation appeared from the German edition by Pro­fessor D. W. Thomson. In 1904 Pavlov was awarded the Nobel Prize

16 Obituary Notices

for Medicine for his work on the physiology of digestion. By this time, however, Pavlov had practically given up a direct personal interest in digestion and had taken up the subject of conditioned reflexes.

At the age of 58, when Pavlov was already in the highest rank of physiologists and when, had he stopped work completely, he would still have remained one of the greatest scientists of his time, he gradually embarked on possibly a still greater scientific adventure. The study of salivary glands led him to the investigation of what was then known as “ psychical ” secretion of digestive juices. This secretion he began to study with the same ultra-materialistic approach as any other activity of the organism. At first without any definite plan, treating this secretion more from the point of view of digestive utility, he gradually began to realize that it could be used as a new approach to the study of the highest functions of the cerebral cortex. The salivary glands, instead of being of interest in themselves, now were used as an index of the com­plicated phenomena taking place in the brain. The appetite reactions which so interested him while working with sham-feeding, and which became so familiar to him during his digestive work, now were used as an objective sign of cortical reactions. These reactions he treated like any other reflexes, just as Sherrington did for the spinal cord and Magnus for the brain stem. The brain which even now to many has a sort of undefined, vitalistic, almost mystical aspect, was treated by Pavlov in the same manner as other organs of the body. In studying the activity of the cortex, Pavlov never pretended to become a psychologist, he re­mained a pure physiologist and rather scorned the attempts of psychology to intrude into the physiological aspects of brain activity. In fact, he i says “ it is still open to discussion whether psychology is a natural science or whether it can be regarded as a science at all. Every material system can exist so long as its internal forces, attraction, cohesion, etc. . balance the external forces acting upon it. This is true for an ordinary stone just as much as for the most complex chemical substance, and its truth should also be recognized for the animal organism. Reflexes are the elemental units of this perpetual equilibration ” . These reflexes Pavlov soon realized were of two types. Reflexes which are constantly present under any conditions of the animal’s existence—in Pavlov’s terminology unconditioned reflexes—and reflexes which are acquired during the animal’s individual existence, which are, so to speak, learnt and which are rigidly dependent on internal and external conditions— conditioned reflexes. In the higher animals these reflexes naturally assume the highest importance by determining the behaviour of an individual. The phenomena of education and the adjustment of the

Ivan Petrovich Pavlov 17

individual within the environment, in fact, his whole social existence, depend on these learnt or conditioned reflexes.

From about 1905 to the end of his life Pavlov devoted himself to the study of these reflexes. A new important chapter of Physiology had been created. The results obtained have to a large extent influenced and modified the old physiology of the brain, the physiology of the sense organs, and also the science of psychology and even psychiatry.

Problems of development of learnt reactions and of their disappearance, the interaction between various conditioned reflexes, their relation to unconditioned reflexes, physiological processes underlying the phenomenon of discrimination of stimuli, the problems connected with the hypnotic state and sleep, the effect of various drugs on conditioned activity, localization of functions in the cortex, the limits of discrimination of stimuli by different sense organs, the pathology of conditioned reflexes such as experimental neuro-psychoses and their treatment, all these aspects of cortical activity were subjected to detailed investigation. The results of this colossal work only gradually penetrated abroad from Russia. General reviews of the subject were given by Pavlov at the meetings of International Physiological Congresses. They were, however, usually given in the form of a general discussion and hardly conveyed to the audience sufficient information about the method itself and the results achieved to allow of a real appreciation of the importance of the new subject. I t was only after the translation of his two books on conditioned reflexes that the subject became generally known. To-day the method of conditioned reflexes has been recognized all over the world. Institutes have been built for the special purpose of continuing and expanding Pavlov’s work.

Pavlov’s long scientific career appears like that of two great minds, one growing out from the other : Pavlov, the father of modern knowledge of digestion, and Pavlov, the creator of a still greater branch of physiology, that of conditioned reflexes.

Professor Pavlov was elected a Foreign Member of the Royal Society in 1907 and an Honorary Member of the Physiological Society in 1909. The Royal Society awarded him the Copley Medal in 1915. In 1928, when he visited this country for the Harvey Tercentenary celebrations, he gave a Croonian Lecture before the Royal Society on conditioned reflexes. At a dinner meeting of the Royal Society Club on that occasion Pavlov told his English friends that he had first been attracted to the study of physiology, even before the beginning of his University course, through reading a Russian translation of a book by an Englishman, George Henry Lewes, on the Physiology of Common Life. His last visit

OBIT. c

18 Obituary Notices

to this country, at the age of 85 and about seven months before he died, was in order to attend the International Neurological Congress in London where he spoke about neuroses and psychoses from the point of view of conditioned reflexes. A few weeks later he presided over the Inter­national Physiological Congress held in Russia, where he received for the last time in his life the enthusiastic and affectionate applause of physiologists from every civilized country. The aged Pavlov, still a romantic, now almost a legendary figure, still engagingly simple and boyishly humorous, a little impatient with this popularity, received his last ovation. Within a few months he died from pneumonia after a short attack of influenza.

G. V. A n r e p .