DIGESTION AND ABSORPTION IN THE INTESTINES. 705 



The Digestive Action of Pancreatic Juice. The digestive 

 action of the secretion depends upon the three enzymes trypsin, 

 diastase (amylopsin), and lipase. The specific effects of each 

 may be considered separately. 



Action of Trypsin. The activated trypsinogen causes hydrolytic 

 cleavage of the proteid molecule in a manner analogous to that 

 described for pepsin. Its action differs from that of pepsin, however, 

 in several respects. It attacks the proteid in neutral as well as in 

 slightly acid or markedly alkaline solutions. Its effect upon the 

 proteid is more rapid and powerful than that of pepsin and the 

 proteid molecule is broken up more completely. As was said in 

 describing the action of pepsin, it and the trypsin really act 

 together, the change begun by the pepsin is completed by the tryp- 

 sin. The preliminary action of the pepsin not only hastens that of 

 the trypsin, but to some extent alters it; a proteid submitted first 

 to pepsin and then to trypsin is more completely broken up than if 

 the trypsin acted alone. The steps in the hydrolysis of the proteid 

 molecule by trypsin have been the subject of a very great amount of 

 study, and views as to the details have changed somewhat rapidly 

 of recent years. Kuhne supposed that the proteid molecule contains 

 two groups, the hemi and the anti. Under the influence of the trypsin 

 these are, on his theory, converted into corresponding proteoses, 

 primary and secondary, and then into peptones, hemipeptone and 

 antipeptone. As distinguished from the pepsin, the trypsin hy- 

 drolyzes the hemipeptone still further, splitting it up into a number 

 of much simpler crystalline bodies, such as leucin, tyrosin, etc. 

 Antipeptone, on the contrary, resists further hydrolysis, and among 

 the end-products of a prolonged pancreatic digestion some peptone 

 is always found. This view has not been supported by recent work. 

 After a prolonged pancreatic digestion no peptone or peptone-like 

 body can be found; in fact, no substance which gives a biuret reac- 

 tion. Under such conditions the proteid molecule is broken up very 

 completely into a surprising number of smaller molecules, many 

 of which have been identified, while some have as yet escaped de- 

 tection so far as their chemical structure is concerned. The actual 

 products formed depend on the length of time the trypsin is allowed 

 to act and the conditions, favorable or unfavorable, under which it 

 acts. The end-products usually obtained most easily are tyrosin, 

 leucin, aspartic acid, glutaminic acid, tryptophan, lysin, arginin, 

 histidin. The first two of these substances have been known for a 

 long time, and may be obtained easily in crystalline form from 

 pancreatic digestions. If the trypsin is allowed to exert its complete 

 action upon the proteid the end-products are closely similar to those 

 obtained by boiling proteid with acids. The hydrolysis caused 

 by the acids and by the trypsin seems to be nearly identical. The 

 45 



