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A MANUAL OF VETERINARY PHYSIOLOGY 



side is secreting, while its fellow is practically resting. When 

 the rhythm of mastication changes over to the opposite side, the 

 parotid on that side becomes active, while the other passes into 

 the condition of comparative rest. The parotid of the side on 

 which the animal is masticating will secrete two, three, or four 

 times as much saliva as its fellow. The following table shows 

 one of Colin's experiments on the horse : 



So far, these observations apply both to the horse and ruminant, 

 but differences soon occur. When the horse is no longer eating, 

 the parotids stop secreting, but with the ruminant this is not the 

 case : the parotids continue to act, not only during rumination, 

 but during abstinence. During rumination the secretion is 

 unilateral in the sense that very much more is obtained from the 

 side on which the jaws are active. 



The secretion from the submaxillary and sublingual glands 

 behaves quite differently to that of the parotid. It is constant 

 from both sides in all herbivora, no matter what the direction 

 of mastication may be. The submaxillary glands cease to secrete 

 during rumination ; the sublingual is not affected by this function. 



The actual amount of fluid secreted daily from these glands in 

 the large herbivora is astonishing. Colin put it down at 5 to 

 6 kilogrammes (8J to 10J pints) hourly for the horse during 

 the seven hours he is engaged in feeding. He gives the total 

 daily secretion for the animal at 42 kilogrammes (9 J gallons), 

 while for the ox it is still higher — 56 kilogrammes (12 J gallons), 

 of which from 800 grammes (1-4 pints) to 2,400 grammes 

 (4J pints) are produced per hour during the intervals of feeding. 



The submaxillary secretion is placed at 280 grammes (1 \ pints) 

 per hour, and the sublingual at 18 to 20 grammes (f ounce) per 

 hour. 



It is obvious that the amount of secretion depends upon the 

 character of the food ; only half the daily mean is secreted if 

 green food be given, and only one-third if roots form the diet. 

 On the other hand, oats increase the amount secreted. Hay 

 absorbs four times its weight of saliva, oats a little more than 

 their weight, and green fodder half its weight. 



The use of the saliva in herbivora is to assist in mastication 



