112 INSALIVATION. 



waters/ that is to say, saliva is secreted when dainty food is 

 presented to him, especially if the individual is hungry, but 

 this does not occur in the horse. The secretion of the paro- 

 tid glands is totally suspended when the horse is not masti- 

 cating, and only occurs from the gland on the side on which 

 the teeth are grinding during the act of mastication. In the 

 ox the secretion is constant, though very slow when the jaws 

 a,re at rest. Dry food leads to an active flow of salivary 

 secretion, which amounts to five or six times more than when 

 green or wet food is eaten. The submaxillary glands secrete 

 abundantly when the material taken into the mouth has an 

 agreeable taste, and great in proportion as the animal re- 

 lishes the food. Thus Colin found that in eating hay, a 

 horse secreted from 17 to 38 grammes in 15 minutes from 

 one gland, whereas 50 grammes flowed when the animal was 

 allowed corn. The sublingual gland in the horse secretes 

 constantly. 



The salivary glands act under the influence of the nervous 

 system, and though the parotids have been regarded as 

 secreting from compression due to the movements of the jaw, 

 Borden has shown that such is not the case, and that this is 

 due to nervous influence. A similar cause leads to a secre- 

 tion of saliva when the stomach is stimulated to secrete, 

 or when materials possessed of taste are taken into the mouth. 

 Various interesting experiments have been performed to 

 show that these glands are brought into play by stimuli, 

 which operate through the nerves and nervous centres. 



CHEMICAL CONSTITUTION OP SALIVA. The parotidean 

 saliva is alkaline, and has a slightly saltish taste. It is 

 watery, and according to Lassaigne, has a density of 1-0108 

 in the cow, 1-0045 in the horse, and 1-0102 in the sheep, at 

 a temperature of 150 centigrade. The chemical constitution 

 of the same secretion is as follows : 



