NUTRITION 245 



animal begins to die the moment it begins to live. The 

 function of nutrition, therefore, is constructive, while 

 motion and sensation are destructive. 



Another source of demand for food is the production 

 of germs, to propagate the race, and the nourishment 

 of such offspring in the egg and infantile state. This 

 reproduction and development of parts which can main- 

 tain an independent existence is a vegetative phenome- 

 non (for plants have it), and is a part of the general 

 process of nutrition. But it will be more convenient 

 to consider it hereafter (Chapters XXIL, XXIII.). Still 

 another necessity for aliment among the higher animals 

 is the maintenance of bodily heat. This will be treated 

 under the head of Respiration. 



For the present, we will study nutrition, as mani- 

 fested in maintaining the life of an adult individual. 



In all animals, this process essentially consists in the 

 introduction of food, its conversion into tissue, its oxida- 

 tion, and the removal of worn-out material. 



1. The food must be procured, and swallowed. (In- 

 gestion.) 



2. The food must be dissolved. (Digestion.) 



3. The nutritive fluid must be taken up, and then dis- 

 tributed all over the body. (Absorption and circulation.) 



4. The tissues must repair their parts wasted by use, 

 by transforming a portion of the blood into living mat- 

 ter like themselves. (Assimilation.) 



5. Certain matters must be eliminated from the blood, 

 some to serve a purpose, others to be cast out of the 

 system. (Secretion and excretion.) 



6. In order to produce work and heat, the food must 

 be oxidized, either in the blood or in the tissues, after 

 assimilation. The necessary oxygen is obtained through 

 exposure of the blood to the air in the lungs. (Respira- 

 tion in part.) 



