342 VETERINARY PHYSIOLOGY 



the piston of a pump sucking in the water. If an opening be 

 made in the cheek above the level of the water so that air 

 gets in water cannot be sucked up. When drinking, the 

 head is extended, and there is a forward movement of the 

 ears as each gulp is swallowed. The reason for this peculiar 

 backward and forward movement of the ears in the horse 

 when drinking is unknown. 



Mastication and Insalivation. — The process of mastication 

 is very completely performed, the animal taking about five 

 to ten minutes to eat a pound of corn and about fifteen to 

 twenty minutes to eat the same amount of hay. As in the 

 ruminant, mastication is chiefly a side-to-side movement and 

 is unilateral, the parotid gland on the chewing side being 

 the more active. 



The parotid gland is relatively large in the horse, being 

 about twice as large as that of the ox. Unlike the ruminant 

 where the parotid secretion never ceases in health the gland 

 is only active during mastication. The saliva probably con- 

 tains ptyalin. 



The quantity of saliva secreted has been measured by 

 making an oesophageal fistula and collecting the boluses of 

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

 which has been secreted in the mouth. About 40 to 50 

 litres may be produced in a day. The amount is determined 

 by the dryness of the food. Dry fodder absorbs about four 

 times its weight of saliva ; green fodder about half its weight. 



In abdominal pain there is complete cessation of all the 

 salivary glands, and the mouth and tongue become dry. 



Stomach. — In the horse the process of gastric digestion 

 differs from that of carnivora in the following particulars. 



In the first place, the horse has to eat a very large quantity 

 of food in proportion to the size of its stomach, and it is found 

 that part of the food begins to pass very rapidly through the 

 stomach into the intestine. Colin found, when he killed a 

 horse which in two hours had eaten 2500 grms. of hay, that 

 the stomach contained only 1000 grms. But while this is 

 the case, a small residue of the meal remains for a very long 

 time in the stomach, and passes out only when the next meal 

 is taken. 



