102 



HUMAN PHYSIOLOGY 



the presence of these two nervous systems, we come 

 face to face with what may be termed the principle 

 of the division of labour as re- 

 presented in the government of 

 the body. The brain system exer- 

 cises all those functions which are 

 especially associated with volun- 

 tary movements and the exercise 

 of the will. The power, in other 

 words, of doing as we like, depends 

 upon our possession of this nervous 

 system whereby the commands 

 which the brain sends forth are 

 capable of being executed by the 

 body at large, whilst in the same 

 way, information conveyed by the 

 senses from the outer world to 

 the brain can be appreciated, and, 

 if necessary, acted upon by the 

 body. The sympathetic system, 

 on the other hand, may be de- 

 scribed as the " involuntary" nerv- 

 ous system. It cannot be directly 

 brought into play by the exercise 

 of the will, but can only be stimu- 

 lated indirectly, as, for example, 

 when we take food into the 

 stomach, the movements of the 

 organ, regulated by the nervous 

 Fig. 29. system, being thus stimulated. 



SPINAL CoR A i^ Actions, of which a very consider- 

 THE CEREBRO- able number are performed by the 

 SPINAL SYSTEM. body> such as are more or less 



of automatic or machine-like character, are regulated 

 and supervised by the sympathetic system. For 



