82 ORGANIC FUNCTIONING 



to the higher mammals. But essentially the same processes can 

 be said to occur in all animals having an alimentary canal and even 

 in the ccelenterates and protists analogous enzymatic activities 

 proceed. Of course the enzymes themselves are not quite the 

 same in all animal forms. Thus the herbivores digest cellulose 

 to an extent that does not characterize the digestive processes of 

 the carnivores. 



Digestion in the mouth. The digestive fluid is the saliva, which 

 contains much mucin. It makes the " bolus " of masticated food 

 which is swallowed. But it contains the amylase ptyalin. This 

 converts starchy substances into soluble sugars, mainly maltose. 



Digestion in the stomach. The fluid is the gastric juice, which 

 contains about one-third per cent, of hydrochloric acid and the 

 protease pepsin. There is a substance called pepsinogen in the 

 mucous membrane of the stomach-wall and this is set free, in 

 some way, by the action of CO 2. The pepsin acts on the emulsi- 

 fied fats to some extent (thus it contains a lipase), but mainly it 

 converts proteins into " acid-albumen," proteoses, albumoses 

 and peptones. It may (to a limited extent) split up the latter 

 substances into amino-acids. It does not digest nucleins. 



Digestion in the small intestine. The active fluids are pancreatic 

 juice, intestinal juices and bile. The pancreatic juice contains 

 a lipase called steapsin, an amylase called amylopsin and a protease 

 called trypsin. The trypsin has a precursor, trypsinogen, and this 

 is activated by the enter okinase of the duodenum. 



Steapsin splits up fats into the constituent fatty acids and 

 glycerol. Amylopsin dissolves starchy substances by converting 

 them into maltose and other sugars. Trypsin does much the same 

 things that pepsin does but carries the transformation of proteins 

 further. Finally, in the intestine the peptides, etc., that have 

 been formed by the action of pepsin become largely split up into 

 amino-acids. 



The bile-salts emulsify neutral fats, which, in this state, are 

 more readily attacked by the amylase of the pancreatic juice. 



The bacteria of the large intestine. Incredibly great numbers 

 oi Bacilli {B. coli is the type) live in the large intestine of mammals 

 (and in corresponding parts of the alimentary canals of other 

 vertebrates). They *' deaminize " amino-acids, that is split oiT 

 ammonia. Thus " proteid fragments " (such as leucine, tyrosine, 



