CHAPTER IX. 



GENERAL PHENOMENA OF NUTRITION. 



Nutrition is the name applied to all those processes by 

 which the organism maintains its existence as an individual. 

 In the more degraded forms of life nutrition is a com- 

 paratively simple process ; but, in accordance with the law 

 of the specialisation of functions, it becomes a very com- 

 plicated matter in the higher forms. It is unnecessary to 

 say that it is impossible here to examine the different modes 

 in which nutrition is effected in different organisms ; and all 

 that can be attempted will be to give a very brief and 

 general sketch of the process as a whole. 



Every vital act in every organism appears to be effected 

 at the expense of the structure by which the act is performed. 

 Whenever a muscle contracts — thus performing its proper 

 function — a portion of its substance is destroyed ; and this 

 holds good of every tissue and of every function. It follows 

 from this that life is accompanied by constant but partial 

 death of the matter of life; and the more actively and 

 perfectly any organism exercises its vital functions, the more 

 rapidly does it destroy the material basis by which the 

 vitality is manifested. It follows, also, from this, that the 

 constant loss of substance caused by the exercise of vital 

 acts must be as constantly repaired, if the organism is to 

 maintain its integrity. This can only be effected by the con- 



