USES OF SALIVA. 269 



to three ounces ; and the saliva collected from the mouth 

 during the same period, and derived from the other sali- 

 vary glands, amounted to six times more than that from 

 the one parotid. 



The purposes served ly saliva are of several kinds. In 

 the first place, acting mechanically, it keeps the mouth in 

 a due condition of moisture, facilitating the movements of 

 th tongue in speaking, and the mastication of food. 

 (2). It serves also in dissolving sapid substances, and ren- 

 dering them capable of exciting the nerves of taste. But 

 the principal mechanical purpose of the saliva is, ( 3), that 

 by mixing with the food during mastication, it makes it a 

 soft pulpy mass, such as may be easily swallowed. To 

 this purpose the saliva is adapted both by quantity and 

 quality. For speaking generally, the quantity secreted 

 during feeding is in direct proportion to the dryness and 

 hardness of the food : as M. Lassaigne has shown, by a 

 table of the quantity produced in the mastication of a 

 hundred parts of each of several kinds of food, thirty 

 parts suffice for a hundred parts of crumb of bread, but 

 not less than 120 for the crusts ; 42-5 parts of saliva are 

 produced for the hundred of roast meat; 3-7 for as much 

 of apples ; and so on, according to the general rule above - 

 stated. The quality of saliva is equally adapted to this 

 end. It is easy to see how much more readily it mixes 

 with most kinds of food than water alone does ; and 

 M. Bernard has shown that the saliva from the parotid, 

 labial, and other small glands, being more aqueous than 

 the rest, is that which is chiefly braided and mixed with 

 the food in mastication; while the more viscid mucoid 

 secretion of the submaxillary, palatine, and tonsillitic 

 glands, is spread over the surface of the softened mass, to 

 enable it to slide more easily through the fauces and 

 oesophagus. This view obtains confirmation from the 

 interesting fact pointed out by Professor Owen, that in 

 the great ant-eater, whose enormously elongated tongue 

 is kept moist by a large quantity of viscid saliva, the sub- 



