RECENT WORK ON PROTEIN-HYDROLYSIS 443 



much less uniform, showing such differences that it is possible 

 to arrange the individual cases into two groups, thus: 



(a) Those in which it is limited to an acid reaction ; 

 yeast, mushroom, malt, Nepenthes. 



(b) Those in which it also occurs with an alkaline re- 

 action ; papain, bromelin, hyacinth bulb. 



The work of Vines on the existence of erepsin in plants 

 does not stand alone, for Delezenne and Mouton have discovered 

 it in certain fungi belonging, like the mushroom, to the group 

 of the Basidiomycetes. 



We find thus that there is a considerable body of evidence 

 pointing to the conclusion that trypsin as a distinct enzyme 

 has no existence in plants, but that what has hitherto been 

 described under that name is really a mixture of a pepsin and 

 an erepsin. This does not imply an identity between such 

 pepsin and the similarly named enzyme of the animal stomach. 

 Indeed, we must admit that the names pepsin, erepsin, etc., 

 apply, not to individual enzymes, but rather to groups of them, 

 consisting of several members which show certain differences 

 among themselves, differences which affect only the conditions 

 of their actions, and not the ultimate products of their activity. 



As this indicates a considerable probability in the case of 

 the vegetable proteases, there arises at once a question as 

 to the nature of the trypsin of the animal organism. Is this 

 also a mixture of some member of the pepsin group with an 

 erepsin ? On this point it would be premature to make a 

 definite pronouncement, but there are certain facts apparently 

 having a bearing on the point which claim attention. 



It has been put on record by several observers, some of 

 them writing many years ago, that under certain conditions 

 the pepsin of the stomach seems to have the power of producing 

 amino-acids. Lubavin in 1871 digested proteids with pepsin 

 for considerably longer than a week, and stated that leucin and 

 tyrosin occurred among the products he obtained. Winternitz 

 in 1899 found the tryptophane reaction given after an extract 

 of the stomach of the pig had acted on fibrin for seven hours. 

 These experiments were noteworthy as showing the result of 

 prolonged peptic digestion. They have been amply confirmed 

 by the researches of several physiologists in 1901 and succeeding 

 years. Laurow, Salaskin, Zunz, Langstein, Malfatti, Glaessner, 

 all speak of the formation by either the tissue of the stomach 



