ANIMAL FUNCTIONS. 93 



85 nature never furnishes any organs but such as are abso- 

 lutely necessary, so the terminations of the wings of 

 birds, instead of being furnished with bones and mus- 

 cles which have the prehensile power, like the hand, are 

 only provided with such as are fitted for the insertion of 

 quills. 



PART III. 



ANIMAL FUNCTIONS. 



264. THE Vital Functions, or actions of animals, are 

 such as are immediately essential to life, as the circulation 

 of the blood, respiration, secretion, and absorption. With- 

 out these the animal cannot exist. The Animal Functions 

 are those which support and renovate the system, and 

 without which the vital functions could not long be 

 maintained, as digestion, nutrition, and the formation of 

 chyle. These are not immediately essential to life, but 

 may be suspended for a time. The Mechanical Func- 

 tions are such as depend on the will, as the action of the 

 muscles, whether employed for the purposes of swim- 

 ming, flying, or walking. The instruments by which 

 mechanical action is effected have been the chief sub- 

 jects of the foregoing pages, and we shall now proceed 



What are the vital functions of animals ? What are the animal func- 

 tions ? What are the mechanical functions ? 



