1 88 ORGANIC AGRICULTURAL CHEMISTRY 



may take place in the stomach, it is mostly accomplished in the 

 small intestine and approximately 90 per cent of the digested 

 food is absorbed here before the food mass passes on to the 

 large intestine. The protein digestion products are absorbed 

 into the blood capillaries and, like the carbohydrate products, 

 enter the portal vein. 



The fats are hydrolyzed by pancreatic lipase, steapsin, into 

 glycerol and fatty acids. The fatty acids are converted into 

 soluble, diffusible soaps by the alkalies of the bile and intestinal 

 juice. These soaps are diffusible and are absorbed through the 

 cell walls, entering the lymphatic circulation and thence pass- 

 ing into the blood. Fats are also emulsified by the direct 

 action of the bile and also of the soaps just mentioned. The 

 bile also acts as a stimulator of the steapsin. In the large in- 

 testine there are no enzymes secreted, and, in man, the only 

 digestion occurring takes place in the upper end, and is the 

 simple gradual completion of the digestive processes already 

 mentioned. Absorption of digestion products takes place in 

 the large intestine to some extent, but amounts to less than 10 

 per cent of the digested food material. The absorbed material 

 here follows the same course as that previously absorbed from 

 the small intestine. 



TIME FOR FOOD PASSAGE 



The length of time required for food to be completely digested 

 varies considerably, as would be expected. Small test meals 

 have been known to pass through the stomach in one to four 

 hours, while large meals of meat have required twelve hours. 

 In man the average time is about seven hours for small meals. 

 For the food mass to pass the ileoccecal valve, between the 

 small intestine and the large, requires about nine to twenty- 

 three hours from the time of eating. The three food con- 

 stituents when fed separately pass through the digestive tract 

 with different speeds. Carbohydrates are the most rapid, 

 requiring about four hours, fat about five hours, and protein 



