THE DIGESTIVE PROCESS 29 



fermentation, which decomposes to some extent the 

 albuminoids, carbohydrates, as well as the fibrous 

 part of the food. In this way a horse is enabled 

 to deal with fibrous foods, such as hay and straw, 

 in a fairly effective manner, although not quite so 

 efficiently as ruminants. 



Bacteria are comparatively rare in the stomach 

 and small intestines, as the gastric juice and bile kill 

 most of them off. The gases produced by fermentation 

 in the large intestine are doubtless absorbed into the 

 circulation and exhaled from the lungs. 



Kellner points out that some bacteria have the 

 power of forming albuminoids from amides, probably 

 with the assistance of nitrogen-free substances (carbo- 

 hydrates), and that such albuminoids can be utilised 

 by the animal for the same purposes as the 

 albuminoids in food. Probably this change only takes 

 place in the case of ruminants, as bacterial activity is 

 much greater in their case than with either horses or 

 pigs. 



Absorption of Digested Pood Material. The 

 greater part of the digested food enters the circulation 

 from the small intestines, which have on part of 

 their inner surface a velvety appearance, caused 

 by innumerable hair-like projections called "villi." 

 These have the power of absorbing the digested part 

 of the food. 



The absorbed nutrients find their way into the 

 lymphatic vessels, the branches of which keep collect- 

 ing up until they form ultimately two large ducts, 

 which enter the blood by a vein in the neck. The 

 lymphatics carry the nutrient liquid only in one direc- 

 tion, and act more as tributaries, pouring the absorbed 

 nutrients into the blood at the neck vein. 



