But if one has the historic sense, and knows something of the setting in which such doctrines come to the birth, one cannot regard it as remarkable that men of sense should urge them. No one coins them independently out of his own brain; little by little men are impelled along the path that leads to such conclusions. Plotinus was a careful student of the philosophers that preceded him. He saw that mind must be distinguished from matter, and he saw that what is given a location in space, in the usual sense of the words, is treated like a material thing. On the other hand, he had the common experience that we all have of a relation between mind and body. How do justice to this relation, and yet not materialize mind? What he tried to do is clear, and it seems equally clear that he had good reason for trying to do it. But it appears to us now that what he actually did was to make of the mind or soul a something very like an inconsistent bit of matter, that is somehow in space, and yet not exactly in space, a something that can be in two places at once, a logical monstrosity. That his doctrine did not meet with instant rejection was due to the fact, already alluded to, that our experience of the mind is something rather dim and elusive. It is not easy for a man to say what it is, and, hence, it is not easy for a man to say what it is not. The doctrine of Plotinus passed over to Saint Augustine, and from him it passed to the philosophers of the Middle Ages. How extremely difficult it has been for the world to get away from it at all, is made clearly evident in the writings of that remarkable man Descartes. Descartes wrote in the seventeenth century. The long sleep of the Middle Ages was past, and the several sciences had sprung into a vigorous and independent life. It was not enough for Descartes to describe the relation of mind and body in the loose terms that had prevailed up to his time. He had made a careful study of anatomy, and he realized that the brain is a central organ to which messages are carried by the nerves from all parts of the body. He knew that an injury to the nerve might prevent the receipt of a message, _i.e._ he knew that a conscious sensation did not come into being until something happened in the brain. Nor was he content merely to refer the mind to the brain in a general way. He found the "little pineal gland" in the midst of the brain to be in what he regarded as an admirable position to serve as the seat of the soul. To this convenient little central office he relegated it; and he describes in a way that may to-day well provoke a smile the movements that the soul imparts to the pineal gland, making it incline itself in this direction and in that, and making it push the "animal spirits," the fluid contained in the cavities of the brain, towards various "pores."