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 part of those that occur in the brain? Such distinctions cannot exist among 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 exception among the other bodily organs.
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 readily inferred from the shape of the brain, and the number of creases or folds that extend its surface. But not only does the outward appearance 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 considered the brains, as he contemptuously called them, a mucous substance 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 interlaced. 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 anatomical 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