Page:Popular Science Monthly Volume 85.djvu/38

34 stimuli. The activities, which in lower animals are "cabined, cribbed, confined," reach in man their fullest and freest expression; but the enormous difference between the relatively fixed behavior of a protozoan or a germ cell and the relatively free activities of a mature man is bridged not only in the process of evolution, but also in the course of individual development.

6. Consciousness.—The most complex of all psychic phenomena, indeed the one which includes many if not all of the others, is consciousness. Like every other psychic process this has undergone development in each of us; we not only came out of a state of unconsciousness, but through several years we were gradually acquiring consciousness by a process of development. Whether consciousness is the sum of all the psychic faculties, or is a new product dependent upon the interaction of the other faculties, it must pass through many stages in the course of its development, stages which would commonly be counted as unconscious or subconscious states, and complete consciousness must depend upon the complete development and activity of the other faculties, particularly associative memory and intelligence. The question is sometimes asked whether germ cells, and indeed all living things, may not be conscious in some vague manner. One might as well ask whether water is present in hydrogen and oxygen. Doubtless the elements out of which consciousness develops are present in the germ cells, in the same sense that the elements of the other psychic processes or of the organs of the body are there present—not as a miniature of the adult condition, but rather in the form of elements or factors, which by a long series of combinations and transformations, due to interactions with one another and with the environment, give rise to the fully developed condition.

Finally there seems good reason for believing that the continuity of consciousness, the continuing sense of identity, is associated with the continuity of material substance, for in spite of frequent changes of the materials of which we are composed our sense of identity remains undisturbed. However, the continuity of protoplasmic and cellular organization generally remains undisturbed throughout life, and the continuity of consciousness is associated with this continuity of organization, especially in certain parts of the brain. It is an interesting fact that in man and in several other animals which may be assumed to have a sense of identity, the nerve cells, especially those of the brain, cease dividing at an early age, and these identical cells persist throughout the remainder of life. If nerve cells continued to divide throughout life, as epithelial cells do, there would be no such persistence of identical cells, and one is free to speculate that in such cases there would be no persistence of the sense of identity.

Organization includes both structure and function, and continuity of organization implies not only persistence of protoplasmic and cellular structures, but also persistence of functions, of sensitivity, reflexes,