344 VETERINARY PHYSIOLOGY 



II. Physiology 

 I. DIGESTION IN THE MOUTH 



A. Prehension of Food. In the horse, solid food is taken up 

 by the lips and bitten by the incisor teeth. If the nerves 

 supplying the lips are cut, it becomes impossible for the horse 

 to graze. Water is sucked into the mouth by a pumping action 

 of the tongue, which acts like a piston, and if air is allowed to 

 get in above the lips, water cannot be sucked up. 



In ruminants the tongue plays the important part in collect- 

 ing the hay or grass to be bitten off with the incisors. 



B. Mastication. In the mouth, by the act of chewing, the 

 food is broken up and mixed with saliva. 



Mastication in the horse and in ruminants is chiefly a side- 

 to-side movement, by which the food is ground between the 

 molar teeth. It goes on for some time in one direction, and 

 then takes place for some time in the opposite direction. The 

 parotid gland on the side to which the animal is chewing 

 secretes, while the other is less active. In the horse, the pro- 

 cess of mastication is very completely performed before the food 

 is swallowed, the animal taking about five to ten minutes to eat 

 a pound of corn, and fifteen to twenty minutes to eat the same 

 amount of hay. The teeth in herbivora grow from a permanent 

 pulp, and hence the changes due to this constant growth give a 

 character to the incisors by which the age may be determined. 

 In ruminants the food is chewed later during rumination. 



C. Saliva. The saliva is formed by the salivary glands (viz., 

 the parotid, submaxillary, sublingual, and various small glands 

 in the mucous membrane of the mouth). 



The quantity of saliva secreted by the horse has been 

 measured by making an resophageal fistula and collecting the 

 boluses of food which are swallowed, and so finding the amount 

 of fluid which has been secreted in the rnouth. 



In one horse about thirty-six litres of saliva were produced 

 in twenty-four hours. 



Characters. It is a somewhat turbid fluid which, when 

 allowed to stand, throws down a white deposit consisting of 

 shed epithelial scales from the mouth, leucocytes, amorphous 



