MASTICATION. 51 



when the fodder offers some resistance, by the nippers 

 ( incisor teeth ). The mouthful is then conveyed to the 

 grinders, and is ground by them into a pulp. During this 

 operation it becomes mixed with saliva, which, under the 

 stimulus of the food, flows into the mouth from the 

 different salivary glands. This secretion contains the 

 active principle ptyalin a species of ferment whose 

 office is to convert starch into dextrine (a kind of mucila- 

 ginous starch) and subsequently into grape sugar, in which 

 form it is absorbed by the system. " A large proportion 

 of this albuminous principle is present in the saliva of 

 the horse, but only traces of it exist in that of man" 

 (Carpenter). The amount is proportional to the hard- 

 ness and dryness of the fodder. Lassaigne gives, from 

 experiment, the following results : 



100 parts of dry hay requires 406 parts of saliva, 

 barley 186 

 oats 113 



grass 49 



" Bernard was led to suggest that the submaxillary 

 gland ministers to the sense of taste, whilst the parotid 

 is connected with mastication, and the sublingual with 

 deglutition. The size of the parotid in animals is pro- 

 portionate to the degree in which the mastication of 

 their food is performed. It is large in the horse, which 

 lives on comparatively dry food, less in carnivora, and 

 still less in the aquatic mammals, as the seal. It 

 is absent in birds which swallow their food whole." 

 (Carpenter.) 



The presence of saliva in the food materially aids 



