USES OF SALIVA. 26 1 



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 in conjunction with mucus, 

 it keeps the mouth in a due condition of moisture, facilitat- 

 ing the movements of the tongue in speaking, and the mas- 

 tication of food. (2.) It serves also in dissolving sapid 

 substances, and rendering 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 mas- 

 tication, 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 mas- 

 tication 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 1 20 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, 

 #nd other small glands, being more aqueous than the rest, 

 is that which 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 ob- 

 tains confirmation from the interesting fact pointed out by 

 Professor Owen, that in the great ant-eater, whose enor- 

 mously elongated tongue is kept moist by a large quantity 



