504 DIGESTION. 



The presence of protein or proteoses has, to a certain extent, a pro- 

 tective action on heating an alkaline trypsin solution, and this has 

 been substantiated by recent investigations of BAYLISS and VERNON. 

 The simpler cleavage products have a still greater protective action 

 (VERNON 1 ). Trypsinogen, according to the unanimous statements 

 of several experimenters, is more resistant toward alkalies than trypsin. 

 Trypsin is gradually destroyed by gastric juice and even by digestive 

 hydrochloric acid alone. 



The preparation of pure trypsin has been tried by various experimen- 

 ters. The most careful work in this direction was done by KUHNE and 

 MAYS. Various methods have been suggested by MAYS, but we cannot 

 enter into a discussion of them. A very pure preparation can be obtained 

 by making use of the combined salting out with NaCl and MgSCU. A 

 very active solution, and one that can be kept for a long time (for more 

 than twenty years according to HAMMARSTEN), can be obtained by extract- 

 ing with glycerin (HEIDENHAIN 2 ) . An impure but still very active 

 infusion can be obtained after a few days by allowing the finely divided 

 gland to stand with water which contains 5-10 cc. chloroform per liter 

 (SALKOWSKI) at the temperature of the room. Such infusions can be 

 obtained, nearly free from proteins, by dialyzing with running water after 

 the addition of toluene. 



Like other enzymes, trypsin is characterized by its action, and this 

 action consists in dissolving protein and in splitting it into simpler prod- 

 ucts, mono- and diamino-acids, tryptophane, etc., in alkaline, neutral, 

 and indeed in very faintly acid solutions. This action has been so far 

 considered as characteristic for trypsin. Recent investigations seem 

 to indicate that this action is not due to one enzyme alone, but to the 

 combined action of several enzymes. 



Although contrary to MAY'S statement, there is no question that 

 there occurs in the pancreas besides trypsin, an enzyme similar to erepsin 

 (BAYLISS and STARLING, VERNON 3 ). According to the latter this 

 erepsin has a strong action upon peptone, and he believes that the pep- 

 tone-splitting action of a pancreas infusion is in great part due to the 

 erepsin. The pancreas, besides these, also contains a nuclease (see page 

 493), whose relation to pancreas erepsin has not been determined. 



The unity of trypsin has also been disputed from another point of view. 

 According to POLLAK the trypsin (in the ordinary sense) contains a second 

 enzyme, which does not act upon protein, but only upon gelatin, and he calls 



1 Bayliss, Arch, des scienc. biolog. de St. Petersbourg. 11, Suppl.; Vernon, Journ, 

 of Physiol., 31. 



2 Pfliiger's Arch., 10. 



3 Bayliss and Starling, Journ. of Physiol., 30; Vernon, ibid., 30; and Zeitschr. f. 

 physiol. Chem., 50; Mays, ibid., 49 and 51. 



