156 THE VITAL FUNCTIONS. 



§ 6. Deglntilion. 



The great object of the apparatus which is to pre- 

 pare the food for digestion, is to reduce it into a 

 soft pulpy state, so as to facilitate the chemical 

 action of the stomach upon it : for this purpose, 

 solid food must not only be subjected to mecha- 

 nical trituration, but it must also be mixed with a 

 certain proportion of fluid. Hence all animals 

 that masticate their food are provided with organs 

 which secrete a fluid, called the Saliva, and which 

 pour this fluid into the mouth as near as possible to 

 the grinding surfaces of the teeth. These organs 

 are glands, placed in such a situation as to be 

 compressed by the action of the muscles which 

 move the jaw, and to pour out the fluid they secrete 

 in greatest quantity, just at the time when the food 

 is undergoing mastication. Saliva contains a large 

 quantity of water, together with some salts and a 

 little animal matter. Its use is not only to soften 

 the food, but also to lubricate the passage through 

 which it is to be conveyed into the stomach ; and 

 the quantity secreted has always a relation to the 

 nature of the food, the degree of mastication it re- 

 quires, and the mode in which it is swallowed. In 

 animals which subsist on vegetable materials, re- 

 quiring more complete maceration than those which 

 feed on flesh, the salivary glands are of large size : 

 they are particularly large in the Rodentia, which 

 feed on the hardest materials, requiring the most 

 complete trituration ; and in these animals we 

 find that the largest quantity of saliva is poured 



