The Animal Body Digestion Metabolism. 25 



from the intestine into its walls, and thus enters the body proper, 

 as will be shown in the next chapter. The waste, along with some 

 digested matter and much of the digestive fluids, passes from the 

 small into the large intestine. 



37. Special provision for the horse. The horse, tho eating coarse 

 food like the ox, has a small stomach and no paunch for specially 

 preparing such food for digestion. In partial compensation it has 

 the caecum, which is a greatly enlarged portion of the alimentary 

 tract, linking the small and large intestines. Into the caecum is 

 passed much of the undigested matter, together with the enzymes 

 of the small intestine. Here the digestive processes of the small 

 intestine are prolonged, thus making up for his small stomach and 

 lack of a paunch. 



Since the steps by which the food is prepared thru digestion for 

 final use by the body are so numerous and complicated, it is well to 

 now review the subject, dealing with the nutrients and what occurs 

 with them, rather than considering the organs and solvents em- 

 ployed. 



38. Digestion of fat. As has been stated, the fats of foods, no 

 matter how finely divided, cannot directly enter the circulation, but 

 must be changed in the following manner : One of the enzymes pro- 

 duced by the pancreas is the fat-splitting steapsin, which breaks 

 some of the fats in the food into glycerin and fatty acids. The bile 

 is largely made up of alkaline salts, and with these the fatty acids 

 react and form soaps. These soaps in turn form an emulsion with 

 the unchanged fats, the emulsified fats presenting a large surface 

 on which the steapsin may act. Thus it is believed that the fat 

 which is finally absorbed is split into glycerin and fatty acids, the 

 latter and the alkali of the bile forming soaps. These soaps and 

 the glycerin are absorbed by the intestinal wall, in the cells of 

 which they are reunited into fats and are contributed as such to 

 the circulation. Some authorities hold, however, that a part of the 

 fatty acids and glycerin formed by the splitting of neutral fats by 

 steapsin may be absorbed as such, without being first changed to 

 soaps. 



39. Carbohydrate digestion. The purpose of the animal in di- 

 gesting either starch, or sugars other than those of glucose-like 

 form, is to convert them into glucose or glucose-like sugars, which 

 are the only forms of carbohydrates that can be used in the body. 



