KOSMICOS. To answer your question requires an analysis of Spencer's "Principles of Psychology." You have here on your table the third edition of that work, which received his latest corrections and additions.[116] If you look at the preface of this edition, you will see that, as between Realism and Idealism, he enunciates a view which recognizes an element of truth in each, but rejects the rest. By this "Transfigured Realism" he aims to conciliate what is true in Realism with what is true in Idealism; and it is by this conciliation that he answers the partisans of both systems, who will not sacrifice any part of their respective doctrines. It is important for you to remember this in judging of his psychological system. He begins by a description of the structure and functions of the nervous system, and the nature of nervous actions. Without repeating in all its minute details the structure which he describes, it is enough to say that in all animals, from the lowest to the highest, this peculiar part of the organism which we call the nervous system is composed of two tissues which differ considerably from those composing the rest of the organism. In color they are distinguished from one another as gray and white, and in their minute structures as vesicular and fibrous. In the gray tissue, the vesicles or corpuscles contain a soft protein substance, with granules imbedded in it, consisting of fatty matter. The more developed of these nerve-corpuscles give off branching processes, and the terminations of nerve-fibers are distributed among them. The white tissue is composed of minute tubes containing a medullary substance or pulp, viscid like oil. Imbedded in this pulp, which fills the tubes, there lies a delicate fiber or axis-cylinder, which is uniform and continuous instead of having its continuity broken by fat-granules. This central thread is the essential nerve; and the sheath of medullary matter, and its surrounding membranous sheath, are only its accessories. While, therefore, the matter of nerve-fiber has much in common with the matter of nerve-vesicle, in the latter the protein substance contains more water, is mingled with fat-granules, and forms part of an unstable mass; whereas in the former, the nerve-tube, the protein substance, is denser, is distinct from the fatty compounds that surround it, and so presents an arrangement that is relatively stable.