ANIMAL AND VEGETABLE 



PHYSIOLOGY. 



PART II. 



THE VITAL FUNCTIONS. 



CHAPTER I. 



OBJECTS OF NUTRITION. 



THE mechanical structure and properties of the organized 

 fabric, which have occupied our attention in the preceding 

 volume, are necessary for the maintenance of life, and the 

 exercise of the vital powers. But, however artificially that 

 fabric may have been constructed, and however admirable 

 the skill and the foresight that have been displayed in en- 

 suring the safety of its elaborate mechanism, and in pre- 

 serving the harmony of its complicated movements, it yet of 

 necessity contains within itself the elements of its own dis- 

 solution. The animal machine, in common with every other 

 mechanical contrivance, is subject to wear and deteriorate 

 by constant use. Not only in the greater movements of the 

 limbs, but also in the more delicate actions of the internal 

 organs, we may trace the operation of many causes inevita- 

 bly leading to their ultimate destruction. Continued friction 

 must necessarily occasion a loss of substance in the harder 



VOL. II. 2 



