398 PRACTICAL ORGANIC AND BIO-CHEMISTRY 







IV. Intestinal Juice. 



The cells of the small intestine also produce a secretion the 

 succus entericus which contains erepsin, a peculiar proteoclastic 

 enzyme discovered by Cohnheim ; it acts only upon proteose^ and 

 peptones, converting them into amino acids. This juice also contains 

 invertase and lactase. These enzymes act not only in the secreted 

 juice but also inside the cells of the mucous membrane. Any un- 

 hydrolysed protein or polysaccharide is hydrolysed into its constituents. 



V. Auto lysis. 



Proteoclastic and other enzymes are present in all tissues ; they 

 are concerned in the breaking down of the constituents of the tissue 

 and in their synthesis. 



They are the cause of the auto- or self-digestion of the tissues 

 after death ; in starvation, food is supplied by the breaking down 

 of some organs at the expense of other organs by the autolytic 

 enzymes. 



VI. Putrefaction. 



In the large intestine food remains are acted upon by bacteria. 

 Amino acids are formed from proteins and they are further broken down 

 into amines, carbon dioxide, indole, scatole, hydrogen sulphide, fatty 

 acids. Unabsorbed carbohydrates and fats are also hydrolysed and 

 decomposed. 



VII. The Liver. 



The liver is concerned most intimately with the products formed 

 during digestion in the intestine, especially the monosaccharides and 

 the fats, and with the regulation of their amount in the blood. 

 Monosaccharides, chiefly glucose, are converted into glycogen and 

 retained as reserve food-stuff to be broken down again when the 

 amount of glucose in the blood sinks below its normal limit t to 2: 

 per cent, of glycogen is present in the livers of well-nourished animals, 

 but generally it varies from 'I to '5 per cent. According to Ku'lz 

 the greatest amount is present in the liver 14 to 16 hours after a meal. 

 The fats undergo changes in the liver cells the saturated become 

 unsaturated and they are oxidised to simpler fatty acids and hydroxy 

 acids which circulate in the blood. The amino acids undergo deaminisa- 

 tion in the liver as well as in the other tissues. Liver cells contain 

 arginase, which hydrolyses arginine to urea and ornithine. The liver is 

 additionally concerned in the formation of urea from ammonia and car- 

 bon dioxide ; in birds with that of uric acid as well. It also breaks down 

 the haemoglobin of the blood and excretes the products, bilirubin 

 and biliverdin, into the intestine through the bile duct 



