By Academician Yuri NATOCHIN, Member of Presidium, St. Petersburg Science Center, RAS

Studies of Academician Ivan Pavlov, this outstanding figure of Russian science, raised physiology to an unprecedented height and determined ways of its development for decades ahead. It is no exaggeration to say that Pavlov marks a whole epoch in natural science, in promoting our understanding of the regularities governing the activities of the brain and in dealing with a host of problems in biology and medicine. It was not accidental that he was the first among physiologists to be honored with the Nobel Prize in 1904. What is more, according to the Garfield Index, he is the world's most frequently quoted name in the special literature in his field. As the Dutch physiologist Professor G. Jordan put it, the city of St. Petersburg-former Leningrad-the hometown of Ivan Pavlov-has since become a mecca for physiologists all over our planet.

The name of Academician Pavlov is inseparably associated with the metropolis on the Neva, although he was born in Ryazan in Central Russia (September 14, 1849). The son of a priest, he studied at a theological seminary, but was able to obtain his father's permission to quit it in the final year and enter the University of St. Petersburg. In 1870 he joined the Department of Natural Sciences of the Faculty of Physics and Mathematics, choosing physiology as his main subject.

His choice proved to be a lucky one, and very soon-in 1875-the University Council honored him with a Gold Medal for his thesis "On Nerves Governing the Functioning of the Pancreas". After graduation the promising student decided to continue his studies and entered the Medico-Surgical Academy (since 1881-the Military-Medical Academy). As Pavlov explained later, this was not a change of specialty for the medical career. Having a Degree of Doctor of Medicine, he wanted a leading post at the Chair of Physiology.

Without going into the details of the later years of his life, let me just stress his choice of physiology as his deity which he worshipped and served to the end of his life. Physiologists of my own (post-war) generation had no chance of personal contacts with Ivan Pavlov, but his theoretical con-

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victions, his approach to problems and his search for the solutions of burning problems had a profound effect upon our daily work. As fate would have it, I was able to hear reminiscences about Ivan Pavlov from my own tutors, and his former associates, academicians L. Orbeli*, Ye. Kreps and Corresponding Member of the USSR Medical Academy, A. Ginetsynsky. Their recollections, and those of some leading world scientists, and the most important thing of all-the works of Ivan Pavlov himself-made me feel the atmosphere of that bygone epoch, visualize that remarkable Personality, Scientist and Individual.

He provided a great contribution to our understanding of the mechanisms of digestion, studies of the physiology of blood circulation, higher nervous activity, of the kidneys, of the physiology of the vegetative nervous system and other problems. To him belongs the discovery of the conditioned reflex and the doctrine of higher nervous activity. All of his studies demonstrate his desire to understand the laws governing the functioning of the body systems, organs and tissues as one common complex. With this aim in view Pavlov introduced into medical practice what is known as the chronical experiment which made it possible to study functions of the aforesaid systems using non-anaesthetized animals. (Surgeries were performed for "opening up the window into the inner world" of an organ under investigation.) In this way it became possible to understand the physiological mechanisms of regulation of the functioning of the salivary glands, gastric glands, pancreas, kidneys, etc.

The way I see it, the scientific legacy of Ivan Pavlov rests on one central core-his approach to any body function under investigation as a manifestation of an integral body response to an external or internal impact; to decode in physiological terms the nature of regulations in the body as a single whole; to provide a comprehensive picture concerning their nature-be this digestion, blood circulation or physiological fundamentals of psychic activities. In one of his letters Pavlov put this in the following way: " I am happy that, together with Ivan Mikhailovich Sechenov and the

* See: Ya. Renkas, "The Orbeli Triad", Science in Russia, No. 6, 2002.-Ed.

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host of my dear coworkers, we have acquired for the 'great power' of physiological studies not just half, but the single whole of a living organism. And this is a totally our, Russian, and indisputable contribution to world science, to the universal human thought."

It has been one hundred years since Pavlov's discovery of the mechanism of digestion. And it has been seventy years since his demise. But his principles of physiological analysis have not been "corroded" by the unprecedented progress of research into the phenomena of life in the latter half of the 20th century. What is more, he heralded a whole new era which, as he put it in his speech back on October 23, 1897-"should replace our present physiology of organs and can be regarded as a herald of the final stage in the science of life-physiology of the living molecule".

In the last quarter of the 19th century Ivan Pavlov made one more outstanding discovery. While studying the mechanism of regulation of functions of the heart, which is usually seen as a balance of the stimulating and suppressive impulses (stimulation of sympathic nerves increases the rate of heartbeat, and that of the parasympathic nerves-slows it down), he discovered yet another nerve branch attached to the heart. Later on it was called trophic nerve and it was established that, when stimulated, it boosts the force of cardiac contractions. This fact provoked a years-long dispute about the functional role of the branches of the sympathic nerve which link with the central nervous system (apart from the heart) a number of other organs, including those attached to the nerve fibers of the skeletal muscle. As a result, the concept of what was called the adaptative-trophic function of the nervous system was formulated. This area of research was associated in many respects with the works of Pavlov's disciple-Academician L. Orbeli and his school.

The problem of modulation (natural modification) of body functions received a new turn some time ago in connection with the discovery of different types of membrane receptors for one and the same hormone, or mediator* of the nervous system. As has been established, one of the subtypes of the receptors can act as a trigger of the effect, and, with the participation of the intracellular system of secondary mediators, it can either stimulate the function or inhibit it. As has been demonstrated by my own lab at the RAS Institute of Evolutionary Physiology and Biochemistry named after I. Sechenov, another subtype of the receptor can cause the modulation and change the force of the

* Mediators-physiologically active substances by means of which contact intercellular interactions are produced in the nervous system.- Ed.

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reaction. These cell reactions, however, involve different, or secondary mediators. As a result we get a function adequate to the body requirements for its adaptation to the current conditions of the environment and also for an optimal response to external stimulation.

On December 1, 1901 Pavlov was elected Corresponding Member of the Russian Academy of Sciences. That same year he was submitted as a candidate for the Nobel Prize. But it was only on October 20, 1904 that he received the award for his discovery of the mechanisms of digestion.

In his speech at the ceremony Pavlov dwelled on a problem which was in the focus of his attention at that time: "Essentially, there is only one thing that interests us in life- our psychical essense. Its mechanism, however, was, and still is shrouded in darkness. All human resources: arts, religions, literature, philosophy and historical sciences-all of these things get together in order to shed light onto this darkness. But there is yet one more powerful resource at man's disposal-natural science with its stringently objective methods. This science, as we know now, scores giant achievements every day."

While assessing the significance of his Nobel Prize in a statement in 1933, the scientist pointed out that it gave him independence, making it possible to devote himself completely to scientific research. Being very sensitive of all things related to science, he turned down a suggestion of his former seminary classmate N. Terskoy, who already held the post of Vice-Director of the Chancellery of the Minister of Railways, to use the prize money for stock-exchange speculations. He replied: "I earned this money by incessant work in science, and science has never had, and will never have, anything to do with the stock-exchange."

In 1907 Pavlov was elected full member of the Russian Academy of Sciences and was put almost at once at the head of the Laboratory of Physiology. Later on, in 1925, he insisted that it be turned into a research institute (now- RAS Institute of Physiology named after I. Pavlov). That was this country's first research center in the field of physiology.

In the 1920s Academician Pavlov was actively involved in the development of studies in comparative physiology. On his initiative a bust of the founder of the science of genetics, Gregor Mendel, was put up in front of the building of the Institute of Physiology.

A fair measure of the integrity of character of Academician Pavlov was his insistence on an even approach to both scientific and social problems. The absolute standard in all of his deeds and actions was his ethical and civic position. Thus in 1917, while considering the consequences of the October Revolution, he was hopeful that there will be no repetition of what he called the great sin of the French who sent to the guillotine the great chemical scientist Antoine Lavoisier. He was even refused a stay of execution in order to complete his important experiments and was told that the Republic had no need for scientists and their experiments. To the end of his days Academician Pavlov kept reminding the Soviet authorities of what he called "the eternal regal role of science in human life".

On May 27,1918, the scientist resolutely protested against the dismemberment of our country. As soon as the revolu-

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tion took place, he wrote, we all fell apart, turned our backs to one another with everyone wishing to be on his own. What good will this make, he kept asking his fellow-citizens?

Academician Pavlov highly valued the importance of what he called the scientific idea. He was an active and emotional champion of the freedom of scientific quests, of an independent status of the Academy and free elections of its members. In the late 1920s the country's leadership decided that members of the Communist Party be represented in the USSR Academy of Sciences. To achieve this objective, and contrary to the Charter of the Academy, it was decided that the elections of new Academy members should be conducted not on a personal basis but by electoral roll. And although representatives of the powers that be and some of his own colleagues urged Academician Pavlov to compromise, he never accepted the proposed innovations.

The founding father of the teaching on the higher nervous activity and of the corresponding scientific school, Academician Pavlov lectured for many decades to students of the Military-Medical Academy. Set up in 1917 on his initiative in Petersburg was the Society of Physiologists named after I. Sechenov and the Russian Physiological Journal. Over many years he headed the Society of Russian Doctors in Petersburg always stressing the importance of physiology as the foundation of medicine.

Ivan Pavlov was both-an ardent researcher and an enthusiastic collectioner. In his memorial apartment on the 7th Line Street of the Vasilyevsky Ostrov district in St. Petersburg one can see to this day his collection of butterflies. And the lyrical qualities of his soul found some fitting poetic expressions, such as his translations of poetry of the famous German poet and writer Heinrich Heine.

Published in 1935 was Academician Pavlov's "Letter to the Youth", which essentially became a kind of his will. He wished to all those who dedicated themselves to science consistency, modesty and passion. The message ended with the words: "For the young ones, as for ourselves, it is a matter of honor to try and live up to the great expectations which our motherland places on science."

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