The Digestive System. 43 



glands, as their name reveals, lie under the tongue. The 

 parotid gland is active only on 'the side on which chewing 

 is taking place. In the horse these glands work only 

 during mastication; in cattle they are secreting continu- 

 ally. Sight and odor of the food do not stimulate the 

 glands. 



Quantity of saliva secreted. The amount of saliva se- 

 creted in twenty-four hours is amazing. In the horse 

 about sixteen and one-quarter pints per hour when eat- 

 ing hay, Colin stating five pounds of hay may be eaten 

 in an hour, and Lassaigre estimates that for each pound 

 of hay, 4.06 pounds of saliva, hence 20.3 pounds or about 

 sixteen and one-quarter pints, one-third less if oats are 

 the food, just one-half the quantity when on green fodder, 

 and one -third if on roots; therefore, it is readily seen that 

 the quantity varies with amount of water in the feed, in 

 fact on the dry ness of the food, not on the starch to be 

 acted upon. Its action is more mechanical (i. e., for the 

 purpose of mixing, softening, etc. ) than chemical. The 

 food is thus rendered easy of shaping into a ball (bolus), 

 in which shape it is passed backward and swallowed. 

 This fluid also aids in tasting foods, and keeps the mouth 

 and teeth clean and moist; great quantities of it descend 

 into the first stomachs of cattle and sheep, the fluid being 

 secreted as soon as food is eaten or masticated. 



Swallowing (deglutition) is quite a complicated process, 

 although seemingly simple. It may be divided into 

 three stages, during the first of which the food is under 

 the control of the will and the food is passed back into 

 the pharynx; in the second stage through the pharynx 

 it is then beyond the control of the will, being only 



