88 THE HUMAN MECHANISM 



When one thinks of the hundreds, perhaps thousands, of 

 movements which the body makes, and of the combination 

 of these movements into definite actions or work, and then 

 reflects that the muscle fibers which execute any movement 

 are thrown into orderly contraction by nerve cells which are 

 themselves commanded by higher nerve cells; that these in 

 turn are marshaled, as it were, by still higher cells when 

 the separate movements they evoke are to be combined into 

 a still more complicated action one begins to appreciate 

 the complexity of the organization of the nervous system. 

 The number of the nerve cells is measured by hundreds of 

 thousands, and their efficiency in directing the working 

 organs of the body, so as to meet the demands of life, de- 

 pends not only upon the integrity of the neurones but also 

 upon the perfection of their organization, that is, their 

 grouping into squads, companies, regiments, brigades, divi- 

 sions, and corps, ready to yield instant and obedient response 

 to the command of the higher officers of the will or to the 

 signals of those pickets the sense organs and their afferent 

 neurones which everywhere guard the outposts and give 

 information of the need for action. 



Moreover, this army of neurones, like any other army, 

 becomes efficient by work, by drilling, by practice, even by 

 battle. Like the soldiers of a regular army the neurones 

 may be overworked and their efficiency as a military body 

 may suffer thereby, but they may also work too little ; 

 the perfection of their development and of then- organi- 

 zation depends on the practice they get with reasonable 

 activity. To this point we shall return ; but meantime 

 the student can safely make the application for himself. 

 Such comparison and such application are not only in- 

 structive but intensely practical in their bearing upon 

 the affairs of everyday life upon that right conduct of 

 life which is the first duty of every man, svery woman, 

 every child. . 



