NUTRITION PROPER. 

 Starch. Water. Sugar (glucose). 



QH io O< + H 2 = C 6 H I2 6 



295 



Its function, then, is the digestion of amyloids. This, 

 of course, takes time. Starches, therefore, are dissolved 

 in the stomach, although the digestive juice is made in 

 the mouth. Ptyalin is far more important in herbivores 

 than in carnivores. 



Ferments. — Ferments are of two general kinds — viz., 

 those, like yeast, that contain living microbes which de- 

 termine decomposition in the fermenting substance, and 

 those, like diastase, that contain no microbes and deter- 

 mine change, but not decomposition. All the digestive 

 ferments are of this latter kind. They are called en- 

 zymes. 



After mastication and thorough insalivation the food 

 is gathered into a bolus, pressed by the tongue into 

 the throat, and swallowed — i. e., it is there seized by 

 the involuntary muscles and hurried into the stomach. 

 There we leave it for the present to take up the 



COMPARATIVE PHYSIOLOGY OF MOUTH DIGESTION IN 

 VERTEBRATES. 



The chemical process of saccharization is precise- 

 ly the same in all vertebrates and probably in all 

 animals. The only important variation is in the me- 

 chanical processes of food-taking and mastication, espe- 

 cially the latter. This brings us to the important 

 subject of 



Teeth in Vertebrates.— We take up this somewhat 

 fully on account of its important bearing on classifica- 

 tion, especially of mammals. The character of the teeth 

 is determined by the food, and the nature of the food 

 determines the habits, and therefore the whole structure 

 of the animal. All the parts of an animal are in har- 

 monic relation with one another. The keynote of this 



