circulation of the blood, and by that remarkable discovery of his he laid the foundation of a scientific theory of the larger part of the processes of living beings—those processes, in fact, which we now call processes of sustentation—and by his studies of development he first laid the foundation of a scientific knowledge of reproduction. But, besides these great powers of living beings, there remains another class of functions—those of the nervous system—with which Harvey did not grapple. It was, indeed, left for a contemporary of his, Réné Descartes, to play a part in relation to the phenomena of the nervous system which is precisely equal in value to that Harvey played in regard to the circulation. You must recollect that this man Descartes was not merely, as some had been, a happy speculator. He was a working anatomist and physiologist, conversant with all the anatomical and physiological law of his time. A most characteristic anecdote of him, and one which should ever put to silence those shallow talkers who speak of Descartes as an hypothetical and speculative philosopher, is, that a friend once calling upon him in Holland begged to be shown his library. Descartes led him into a sort of shed, and, drawing aside a curtain, displayed a dissecting-room full of the bodies of animals in course of dissection, and said, "There is my library."
The matters of which we shall treat are such as to require no extensive knowledge of anatomy. I need only premise that what we call the nervous system in one of the higher animals consists of a central apparatus, composed of the brain, which is lodged in the skull, and of a cord proceeding from it, which is termed the spinal marrow, and which is lodged in the vertebral column or spine, and that then from these soft white masses—for such they are—there proceed cords which are termed nerves, some of which nerves end in the muscle, while others end in the organs of sensation. The first proposition that you find definitely and clearly stated by Descartes is the view that the brain is the organ of sensation, of thought, and of emotion—using the word "organ" in this sense, that certain changes which take place in the matter of the brain are the essential antecedents of those states of consciousness which we term sensation, thought, and emotion. If your friend disagrees with your opinion, runs amuck against any of your pet prejudices, you say, "Ah! poor fellow, he is a little touched here," by which you mean that his brain is not doing its business properly—that he is not thinking properly—thereby implying that his brain is some way affected. It remained down to the time of Bichat a question whether the passions were or were not located in the abdominal viscera. In the second place, Descartes lays down the proposition that all the movements of the animal bodies are effected by the change of form of a certain part of the matter of their bodies, to which he applies the general term of muscle. That is a proposition which is now placed beyond all doubt whatever. If I move my arm, that movement is due to the change of this mass in
