MASTICATION AND DIGESTION. 61 



of the body, should be made to the food of the animal, 

 if it be misapplied with warm clothing, which, by pre- 

 venting radiation, supplements the action of the fatty 

 layer which lies immediately underneath the skin. 

 Hence a judicious addition of clothing may be practi- 

 cally regarded as an addition to the food ; so that, when 

 it cannot be made, more corn ought to be given. In 

 hot weather, the animal will, naturally, require less food. 

 Mastication and Digestion. The long hairs 

 about the horse's muzzle serve him as feelers in the 

 selection of the food which his lips convey into his 

 mouth, aided, when the fodder offers some resistance, 

 by the front teeth (nippers, or 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 the office of 

 which is to convert starch into dextrine (a kind of 

 mucilaginous 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 of saliva 

 secreted during mastication is proportional to the 

 hardness 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 



