74 ABSORPTION 



mentally, in some animals at least, it has been found that 

 the greater part of the fat (60 per cent.) is passed through 

 the epithelial cells and through the stroma of the villi to the 

 central lacteal, which is the beginning of the thoracic duct. 

 The remainder is absorbed by the blood as fatty acid and 

 glycerin. There is, very likely, a synthesis of some of the 

 latter substances in the body of the epithelial cells into neutral 

 fat. The absorption of water and salts by the small intestine 

 is very active, but there is also a secretion of water back into 

 the intestinal lumen, so that the contents remain of the same 

 fluid consistency. Water and salts are absorbed directly 

 by the blood unless excessive quantities are taken, when a 

 portion passes through the lymphatic system, accelerating 

 the flow of the chyle. Seventy to 83 per cent, of the combined 

 jejunum and ileum in dogs have been removed without effect- 

 ing metabolism, showing a wonderful efficiency as a digesting 

 and absorbing organ. In man fully one-half of the small 

 intestine has been removed with ultimate recovery. 



Absorption from the Large Intestine. The absorption from 

 this part of the alimentary tract is considerable, as is shown 

 by changes in its contents, which, entering at the ileocecal 

 valve in a fluid state, are converted into solid feces. Of the 

 15 per cent, protein present some is absorbed and some is 

 destroyed by bacterial action. The absorptive powers of the 

 large intestine have been illustrated by the injection of nutrient 

 enemata consisting of egg albumin, salt, and milk fat. In 

 this case, however, the antiperistaltic movements of the large 

 intestine may pass the food back through the ileocecal sphincter 

 into the small intestine, where an important part of the pre- 

 liminary digestion and absorption may occur. Furthermore, 

 remnants of proteolytic, amylolytic, lipolytic, and inverting 

 enzymes may have been passed into the large intestine, where 

 they continue their work. 



