RECENT WORK ON PROTEIN-HYDROLYSIS 437 



results, and have led to the identification of enzymes strikingly 

 similar to if not identical with those now shown to exist in the 

 animal body. 



It has been known for many years that a great number of 

 proteases exist in plants, though how far they are specifically 

 distinct from each other cannot well be affirmed, on account of 

 the differences in the plants in which they have been found and 

 of certain differences in the conditions of the experiments that 

 have been carried out with them. Most of them act intracellu- 

 larly, only those of the so-called insectivorous plants being 

 formed out of glandular tissues. The best known of them are 

 papain, from Carica Papaya ; bromelin, from Ananas sativa (the 

 pineapple) ; nepenthin from Nepenthes (the pitcher-plant) ; and 

 the trypsins from germinating seeds. When they are compared 

 with the proteases of animal origin they have always appeared 

 to resemble trypsin on the whole rather than pepsin, as, though 

 sometimes working in acid solutions, they have been found to 

 produce amino-acids as well as peptone. Indeed no definite 

 evidence pointing clearly to the existence of a pepsin or pepsin- 

 like enzyme in the vegetable kingdom has been forthcoming. 



The enzymes alluded to had up to the beginning of the 

 century been found in only a limited number of plants, and 

 even in those they were not proved to be widely distributed. 

 The opinion was held, however, by many physiologists that 

 the vegetable organism needed for its ordinary metabolic 

 processes a distribution of proteases as widespead as that of 

 diastases, starch and proteids playing similar roles in its 

 nutrition. The difficulty of finding these looked-for proteases 

 was considerable, as no rapid method of detecting their activity 

 had been hit upon. The idea that they should attack such 

 substances as fibrin or coagulated albumin was always under- 

 lying the method of research. 



The recognition of the existence of tr} r ptophane as a mark 

 of the progress of so-called tryptic digestion was seized upon by 

 Vines, and in his hands became extremely useful as an indication 

 of the existence of proteasic enzymes. With its assistance he 

 succeeded in showing that the latter are very widely distributed, 

 finding them in a very great variety of plants taken from all 

 groups of the vegetable kingdom, and from almost all parts of 

 the plants containing them. 



Many plants, however, gave no evidence of the possession 



