302 VETERINARY PHYSIOLOGY 



as the more fundamental type. It is convenient, therefore, 

 to deal first with digestion in carnivora, and thereafter 

 indicate the modifications that exist in herbivora. Omnivora, 

 e.g. man and pig, present such minor differences from carni- 

 vora that the}^ can be included with these. Indeed, the 

 work done to elucidate the physiology of human digestion 

 has been done mainly on the dog — a carnivorous animal. 



A. DIGESTION IN CARNIVORA AND OMNIVORA. 

 I. DIGESTION IN THE MOUTH. 



(rt) Mastication- 

 In the mouth the food is broken up and mixed with 

 saliva in the act of chewing. Mastication is less perfectly 

 performed in carnivora than in herbivora. The dog 

 masticates very imperfectly. After a tew rapid chews the 

 food is swallowed. 



{h) Insalivation. 



The saliva is formed by the salivary glands — the parotid, 

 submaxillary, sublingual, and various small glands in the 

 mucous membrane of the mouth. 



1. Saliva — (1) Characters. — The Saliva 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 calcic and magnesic phos- 

 phates, and generally numerous bacteria, Its specific gravity 

 is low — orenerallv about 1003. In reaction it is neutral or 

 faintly alkaline. 



(2) Chemistry. — It is found to contain a ver}^ small propor- 

 tion of solids. The saliva from the parotid gland contains 

 only about 0'4< per cent., while that from the sublingual may 

 contain from 2 or 3 per cent. The sublingual and sub- 

 maxillary saliva, in man, is viscous, from the presence of 

 mucin formed in these glands, while the parotid saliva is 

 free from mucin. In addition to mucin, traces of proteins 

 are present, and in certain animals an enzyme — ptyaliii — 

 is associated with these proteins. Ptyalin is present in man 

 and in the pig. It is absent in carnivora. 



