CHAPTER SIXTH. 



NUTRITION. 



200. THE second class of the functions of animals are 

 those which relate to the maintenance of life and the per- 

 petuation of the species ; the functions of vegetative life, (59.) 



201. The increase of the volume of the body must re- 

 quire additional materials. There is also an incessant waste 

 of particles which, having become unfit for further use, are 

 carried out of the system. Every contraction of a muscle 

 expands the energy of some particles, whose place must be 

 supplied. These supplies are derived from every natural 

 source, the animal, vegetable, and even the mineral king- 

 doms ; and are received under every variety of solid, liquid, 

 and gaseous form. Thus, there is a perpetual interchange 

 of substance between the animal body and the world around. 

 The conversion of these supplies into a suitable material, its 

 distribution to all parts, and the appropriation of it to the 

 growth and sustenance of the body, is called NUTRITION in 

 the widest sense of that term. 



202. In early life, during the period of growth, the amount 

 of substances appropriated is greater than that which is lost. 

 At a later period, when growth is completed, an equilibrium 

 between the matters received and those rejected is established. 

 At a still later period, the equilibrium is again disturbed, 

 more is rejected than is retained, decrepitude begins, and at 

 last the organism becomes exhausted, the functions cease, and 

 death ensues. 



203. The solids and fluids taken into the body as food are 



