RECENT WORK ON PROTEIN-HYDROLYSIS 435 



hydrolyses the dextrin to sugar. There has, however, been so 

 far advanced no satisfactory proof of the existence of dextrinase. 

 The occurrence in the same secretion of two enzymes separable 

 with greatest difficulty, if at all, is exemplified by the simul- 

 taneous presence of trypsin and rennin in pancreatic juice. 



Very careful researches have been made by Vernon on the 

 secretions of the pancreas and small intestine during recent 

 years. At the outset he ascertained that while an extract of 

 pancreas possessed the power of splitting up fibrin, and of 

 forming amino-acids from peptone, these two powers did not 

 run in the least degree on parallel lines. Fresh pancreatic 

 extracts in which the tryptic enzyme was present only in the 

 condition of its zymogen, nevertheless possessed the property 

 of decomposing Witte's peptone with great energy, and they did 

 not gain greater power in this direction after the zymogen had 

 been converted into trypsin. The trypsin in the zymogen 

 condition being inert, it necessarily follows that a special pepto- 

 clastic enzyme was present in the extract. 



The coincident occurrence of the two enzymes in the pancreas 

 is supported by the further observation that when extracts of 

 this organ are kept for some time under aseptic conditions, the 

 powers of fibrin digestion and of peptone decomposition do not 

 disappear with the same relative rapidity, but show considerable 

 variation in this respect. If the extract is prepared with 

 glycerine, the tryptic effect is maintained longer than theereptic; 

 if the solvent is dilute alcohol, the reverse is the case. 



Vernon made also a series of experiments on the facility 

 with which the enzymes could be destroyed by the action of 

 alkalis. He had shown previously that trypsin, when exposed 

 to the action of sodium carbonate in as low a percentage as 

 o*4, underwent destruction with considerable rapidity, which 

 was greatly increased as the percentage of the alkali became 

 higher. Erepsin also shows this susceptibility to change under 

 similar exposure. Comparing the two enzymes, he found 

 that when kept at 38 C. in the presence of 0*4 per cent, of 

 sodium carbonate, trypsin is at first more rapidly destroyed than 

 erepsin, and that later, after nine or ten hours, the reverse is the 

 case ; the erepsin being decomposed the faster. 



Another difference between the two was observed in their 

 behaviour with alcohol, pancreatic erepsin being the more 

 readily precipitated. 



