26 Feeds and Feeding. 



Since the carbohydrates constitute a large portion of the food of 

 animals, nature provides for their digestion in several parts of the 

 alimentary tract. Carbohydrate digestion begins with the action 

 of ptyalin on the starches of foods in the mouth, whereby they are 

 converted into maltose. Ptyalin action continues in the first por- 

 tion of the stomach, but ceases in the latter part of that organ. 

 Sugars of glucose form may be absorbed from the stomach. Even 

 the compound cane-, malt-, and milk-sugars may without change be 

 absorbed from the alimentary canal in small amounts. If these 

 compound sugars remain in the digestive tract an appreciable time, 

 as usually happens, they are changed to glucose and glucose-like 

 sugars. Thus most of the carbohydrates are absorbed from the ali- 

 mentary tract in the form of glucose. Nearly all the carbohydrates 

 are carried on from the stomach into the small intestine, which is 

 the principal organ concerned in their final digestion. Here the 

 starches which have escaped digestion in the mouth and stomach 

 are acted upon by amylopsin, and the compound cane-, malt-, and 

 milk-sugars are converted by the invertases into simpler glucose- 

 like sugars. 



When a human eats bread, or an animal consumes hay or corn, 

 the starch of such food must all be changed to sugars before it can 

 enter the body proper. With trifling exceptions all compound sugars 

 are converted into glucose-like sugars. It is even held that milk 

 sugar has no food value with birds, because their digestive tract 

 provides no enzyme for breaking it up into glucose-like sugars which 

 may be absorbed. 



In the digestive tract no enzyme has been found which acts on 

 cellulose. Bacteria inhabiting the alimentary canal, however, at- 

 tack cellulose, especially in the paunch of ruminants and the caecum 

 of the horse. Among the products of such bacterial decomposition 

 of cellulose are organic compounds, such as acetic and lactic acid, 

 besides gases marsh gas, carbon dioxid, and hydrogen. While 

 these gases are of no value to the animal, there is little doubt that 

 the other cleavage products are absorbed from the digestive tract 

 and serve as nutrients. Smith 1 suggests that cellulose digestion 

 may be brought about by ferments contained in the food itself. 

 When artificially digested with strong sulphuric acid, cellulose is 

 converted into a gummy product and finally into glucose. Because 

 the goat and the ox can subsist for long periods on coarse straw, 

 which is largely cellulose, it is reasonable to hold that this sub- 



1 Manual of Vet. Physiol., 1908. 



