110 HUMAN PHYSIOLOGY 



variety of actions, having for their object a definite 

 purpose. We thus arrive at the conclusion that the 

 brain cell is the seat of those actions or processes 

 which are generally spoken of under the name of 

 "thought" and "consciousness," and which are 

 made manifest through the bodily actions. One 

 proof of this fact is found in the phenomena of 

 disease, for, when certain cells undergo degeneration, 

 the power of naturally exercising the brain becomes 

 very much altered, and the responsibility of the 

 individual may, as in cases of insanity, be practically 

 abolished. Here, it would seem, we stand on fairly 

 firm ground in assuming that the brain cell is a 

 generator of that subtle and particular kind of energy 

 to which, in one of its manifestations at least, we 

 apply the name of " thought." Beyond this stage of 

 reasoning it is impossible to proceed with exactitude. 

 What thought is in its essence we do not know. We 

 can merely indicate the apparatus by which this 

 phase of mental action is manifested, namely, by 

 the highest protoplasm or living matter of which 

 brain cells are composed. As we cannot understand 

 the nature of life itself, so we remain ignorant to-day 

 of the precise conditions under which the living 

 matter of the brain cells gives rise to the higher 

 expressions of consciousness. 



How THE NERVOUS SYSTEM ACTS. One general 

 principle is found to underlie the working of this 

 complicated system. To this principle the name of 

 reflex action is given. A simple illustration of the 

 working of the nervous system is afforded in the 

 case of a person withdrawing the head from a blow 

 aimed at him. Here the action he performs begins 

 at the eye, which, like every other organ of sense, is 

 a mere "gateway of knowledge" devoted to the 



