336 FOOD AND DIGESTION 



is an admixture with the secretion of the mucous membrane of the intestine. 

 The succus entericus contains an activating enzyme, enterokinase, which 

 converts the inactive and stable trypsinogen of the pancreatic juice into the 

 active but less stable trypsin. This fact is another of the wonderful series of 

 contributions to the exact knowledge of the subject of digestion made from 

 Pawlow's laboratories. 



Trypsin converts proteids into proteases and peptones. The process is 

 both more rapid and more complete than in gastric digestion, so that, in the 

 final result, the peptones are greatly in excess of the proteoses. The proteids 

 pass through the same preliminary stages as in gastric digestion, being split 

 at first into alkali-albumin, then into primary proteoses, both proto-proteose 

 and hetero-proteose, and then into deutero-proteose. The first stages are so 

 transient that it is difficult to detect either the alkali-albumin or primary pro- 

 teose. The deutero-albumoses are easily demonstrated in the earlier stages, 

 but become very scanty later. Anti-albumid is found as a side product in 

 artificial digestion, but is not present in normal digestion. 



Trypsin also has the power of splitting a certain proportion of peptones, 

 the hemi-peptones, into simpler bodies such as leucin or amido-caproic acid, 

 tyrosin or paraoxyphenyl-amido-propionic acid, lysin, lysatinin, tryptophan, 

 and some other bodies. In the cleavage of the proteid molecule there is prob- 

 ably left a complex nucleus which may yet serve as a synthetic center for the 

 rebuilding of the proteid molecule. This nucleus is called a polypeptid. 

 Leucin and tyrosin have been found in the intestinal contents, so that this 

 destruction of hemipeptone in artificial tryptic digestion must take place to 

 a certain extent within the body as well. 



In laboratory experiments only about one-half of the peptones can be 

 changed in this way. The more stable portion which cannot be changed 

 is usually known as antipeptone. There are several theories as to the reason 

 or use of this change into leucin, tyrosin, etc. One of the most plausible 

 is that it saves the body from needless work when too much proteid food has 

 been taken; the breaking down in the intestine of bodies only slightly removed 

 from urea relieves the liver and other glandular organs from the strain of 

 converting an excess of absorbed proteid material into a form in which it can 

 be excreted. Another theory is that leucin, tyrosin, etc., are essential for 

 the physiological working of the body in some unknown way, just as are the 

 products of the thyroid gland. The formation of the decomposition products, 

 indol and skatol, is caused by the action of bacteria on proteids. The albu- 

 minous or proteid substances which have not been converted into peptone in 

 the stomach, and the partially changed substances, i.e., the proteoses, are con- 

 verted into peptone by the pancreatic juice, and then in part into leucin and 

 tyrosin, etc. 



The ferment trypsin acts best in an alkaline medium, but will act also 

 in a neutral medium, or in the presence of a small amount of combined acid; 



