MASTICATION AND DIGESTION 63 



on comparatively dry food, less in carnivora, and still less in 

 the aquatic mammals, as the seal. It is absent in birds 

 which swallow their food whole." {Carpenter.) The 

 salivary glands of the horse are larger than those of all 

 other animals, except ruminants. 



The presence of saliva in the food materially aids its 

 digestion in the stomach. "Among the experiments are 

 those of Spallanzani and Eeamur, who found that food 

 inclosed in the perforated tubes, and introduced into the 

 stomach of an animal, was more quickly digested when it 

 had been previously impregnated with saliva than when 

 it was moistened with water. Dr. Wright also found that 

 if the oesophagus [gullet] of a dog is tied, and food mixed 

 with water alone is placed in the stomach, the food will 

 remain undigested though the stomach may secrete 

 abundant acid fluid, but if the same fluid is mixed with 

 saliva, and the rest of the experiment similarly performed, 

 the food is readily digested." {Kirhes.) 



Saliva is alkaline, and gastric juice acid. Pancreatic 

 juice and bile are both alkaline. This alternate character 

 seems to have been given to these fluids, so as to regulate 

 their action. 



The chief part of the starch contained in the horse's 

 food passes unchanged into his stomach ; and the action 

 of the alkaline saliva, as a ferment in converting this 

 starch into sugar, ceases on being neutralized by coming 

 into contact with the acid gastric juice. Hence, it would 

 appear that the chief ofi&ce of the saliva is to check undue 

 acidity in the stomach. 



The frothy nature of saliva seems to aid digestion. 

 "The numerous air-bubbles for which saliva is remark- 



