72 THEORY OF FEEDING. 



in order that these constituents may be utilised (assimilated) 

 by the system. These changes are brought about chiefly by 

 certain unorganized ferments (p. 68), which are respec- 

 tively secreted by the digestive glands, and which are 

 characteristic components of the digestive fluids. Digestion 

 commences in the mouth, and does not end until the residue 

 of food quits the body in the form of dung. The action of 

 digestion is not uniform during the progress of the food 

 through the alimentary canal ; for it begins slowly, increases 

 steadily, and having reached its effective limit, it gets slower 

 and slower. Owing to the evolutionary influence of the differ- 

 ent constituents of food, the alimentary canal of animals is 

 more or less divi'ded into tracts (such as the mouth, stomach, 

 small intestine, caecum, and remainder of the large intestine), 

 which are respectively concerned in the digestion of special 

 food substances. Hence the form and particular functions of 

 the alimentary canal are dependent on the natural food. 



DIGESTIBILITY AND WHOLESOMENESS OF FOOD. 



The digestibility of a food is its capability of being 

 absorbed in the system. 



According to Miintz and Grandeau, the respective percent- 

 ages of digestible material contained in the undermentioned 

 foods is as follow : 



Carrots . . . . . . 94.6 per cent. 



Maize . . . . . . . 94.5 ,, ,, 



Bran 93.3 ,, 



Barley 84.5 ,, ,, 



Beans 84.5 ,, ,, 



Oats 75.1 ,,,, 



Wheat straw ...... 49.6 ,, ,, 



Meadow hay ...... 43.3 to 61 ,, 



Despite the theoretical correctness of the above table, we 

 know from experience that oats, especially in large quantities, 

 agree with a horse much better than barley or beans, both 

 of which are put down as being more digestible than oats. 



