THE HISTORY of natural science is a history of discoveries. Yet a discovery connotes more than merely establishment of a hitherto unknown natural phenomenon and its accurate description and explanation. It implies, in addition, a new approach to already familiar phenomena viewing them at a new angle of vision and in previously unsuspected relations and linkages with other phenomena and laws of nature. Such discoveries tend to transform the entire system of views at the subject of research and indeed sometimes change the whole way of thinking in the field of knowledge concerned. The discoveries of Newton, Einstein, Darwin, and Mendeleyev can serve as examples. There is every reason to place in.their class the discovery made by I. P. Pavlov who saw in the phenomenon of"psychic secretion" a special type of reflex inherent in the higher regions of the animal brain--the discovery he heralded to the world in 1902 at the International Congress in Madrid. But in his Madrid speech, I. P. Pavlov did more than merely announce his discovery, he substant iated the possibi l i ty of an exper imenta l physiologic approach to the study of phenomena recognized as psychic. Also, he outlined the basic range of those ideas whose elaboration in later years was to make his name immortal. The world's first physiologist was what he would be named at another international congress, 32 years later. This is not surprising, for I. P. Pavlov was the first scientist to pioneer a physiologic approach to phenomena believed to be the subject of psychology, the science of soul. A n d through his many years of effort, not only did he prove the approach to be valid and fruitful, but originated an entire new field of physiology called the physiology of higher nervous activity. Today I. P. Pavlov is a familiar name to all educated people. But even so the contribution he made to the science of the brain can be hardly appreciated in full unless at least a few words are added about the enormous difficulties met by inquisitive human thought in its attempts to unravel the mysteries of the structure and functioning of the organ of which it was born, and about the crisis existing in the science of the brain by the time the great scholar had made his discovery. Ours is a time of relatively harmonious development in various fields of science and modem man is accustomed to it. So he will perceive as incredulous, as he learns more about the history of science, the millennia-long void of any natural-scientific ideas about the nature of psychic, or higher, brain functions. Indeed, mathematical and physical disciplines attained an impressive level of development even in the ancient world, and many of them are of a standard that makes them still relevant today.* In contrast, the ideas of that time on the structure and functions of the brain were fantastic and controversial to a striking degree. It was not until the 19th century that the stage began to be set for effective physiologic study of the brain. With the progress of electromagnetism, advances were made in the devices used in experiments; upon discovery of the cellular structure of organism, and an encouragement of histologic research, there came a rethinking on the structural principles of various regions in the nervous system; breakthroughs in microbiology led to developing the rules of asepsis and and antisepsis essential for animal survival after an operation on the brain. In the 19th century, key principles for the present physiology of muscles and nerves were formulated (du Bois -Reymond , He lmhol tz , Pfl/iger, Engelmann, B. F. Verigo); studies into spinal reflexes were started (Bell, Magendie, Hall Mtiller, Pfltiger); many of the medulla functions became clear (Flourens, Mtiller, Claude Bernard, F. V. Ovsyannikov, N. A. Mislavsky) as also many functions of the cerebellum (Flourens, Luciani); the centers inhibiting and enhancing the spinal reflexes were discovered (I. M. Sechenov, V. I. Berezin, V. V. Pashutin); and the phenomena of irradiation and summation of excitation (Pfliiger, I. M. Sechenov) and bannung (Exner) were detected. Great success was achieved in the physiology of sensory organs (Helmholtz, Hering, Mach, Weber, and others).