34 THE POPULAR SCIENCE MONTHLY 



tional 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 proto- 

 zoan 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, in- 

 deed the one which includes many if not all of the others, is conscious- 

 ness. 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 conscious- 

 ness 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 undis- 

 turbed. However, the continuity of protoplasmic and cellular organiza- 

 tion generally remains undisturbed throughout life, and the continuity 

 of consciousness is associated with this continuity of organization, espe- 

 cially 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, 



