ACTION OF THE NERVOUS SYSTEM. 63 



blood by means of the assimilation taking place 

 throughout the body. Loss of appetite therefore 

 means a cessation of assimilation. Thus we see that 

 the nervous system controls all the functions of the 

 living body, as a unit. The result of the combined 

 functions of the body, is the sustenance and growth 

 of the body. 



Since growth is controlled by the nervous system, 

 it follows that development also must be to a certain 

 degree controlled by the nervous system ; for de- 

 velopment is either a change in the direction of 

 growth or it implies new growth, i.e. the addition of 

 new material to some part even though the material 

 be taken from an adjacent part. Growth cannot be 

 simply an excess of assimilation above waste. The 

 new material added by growth must form new tissues 

 and new parts. So long as these tissues and parts 

 which are added to an organ, remain of the same 

 nature as the rest of the organ, and cause no consid- 

 erable change of function, the organ is said to grow ; 

 but when the addition of new parts makes the per- 

 formance of new functions possible, then develop- 

 ment is said to occur. A little reflection on the 

 matter will show how arbitrary is the distinction. 

 For no development can take place without growth, 

 and no growth can take place in any organ without 

 modifying in some degree, however slight, the func- 



