66 THE POPULAR SCIENCE MONTHLY. 



be divided into fractions. How, indeed, can one understand that it is 

 permitted to the physiologist to succeed in explaining the phenomena 

 that occur in all the organs of the body, except a pai-t of those that 

 occur in the brain ? Such distinctions cannot exist amoniy vital 

 phenomena. Unquestionably they present very different degrees of 

 complexity, but they are all alike in being either soluble or insoluble 

 by our examination; and the brain, marvellous as those metaphysical 

 manifestations that take place in it appear to us, cannot form an ex- 

 ception among the other bodily organs. 



II. 



From a physiological point of view, those metaphysical phenomena 

 of thought, consciousness, and intelligence, which serve for the various 

 manifestations of the human soul, are nothing but ordinary vital 

 phenomena, and can result from nothing but the action of the organ 

 that expresses them. We shall show that, in fact, the physiology of 

 the brain, like that of all the other bodily organs, is deduced from 

 anatomical observations, from experiments conducted physiologically, 

 and from the teachings of pathological anatomy. 



In its anatomical development the brain follows the general law; 

 that is, it increases in volume whenever the functions which it controls 

 increase in energy. In the graduated orders of animals we find the 

 brain gain in development in proportion to the greater manifestation 

 of intelligence ; and in man, with whom the phenomena of mind have 

 reached their highest expression, the cerebral organ presents the 

 largest volume. The intelligence of the various animals can be read- 

 ily inferred from the shape of the brain, and the number of creases or 

 folds that extend its surface. But not only does the outward appear- 

 ance of the brain change with the modification of its functions ; it 

 presents in its inner structure also a complexity that increases with 

 the variety and intensity of the mental manifestations. As regards 

 the texture of the brain, we are long past the days of Buffon, who con- 

 sidered the brains, as he contemptuously called them, a mucous sub- 

 stance of no importance. The advance of general anatomy and of 

 histology has taught us that the cerebral organ possesses a texture 

 more delicate as well as more complex than that of any other nerve- 

 arrangement. The anatomical elements that make it up are nerve- 

 elements in the shape of tubes and of cells variously joined and inter- 

 laced. These elements are alike in all animals as to their physiological 

 properties and histologic character ; they differ as to their number, 

 net-work, and connection, in a word their arrangement, which in the 

 brain of various species presents a disposition peculiar to each. In 

 this the brain again follows a general law, for in all organs the ana- 

 tomical element has fixed characteristics by which it may be known ; 

 the completeness of the organ consists chiefly in the arrangement of 

 these elements, which presents in every animal species its own peculiar 



