LIXXEAX SOCIETY OF LOXDOX. 6i 



Phytolacca decandra, the only foliage-leaves that I have yet found, 

 out of a large number of plants tried, to digest fibrin. 



I may perhaps digress for a moment to explain that the wide 

 distribution of proteases in the plant-body is now being paralleled 

 by the discovery of a similar distribution in the animal body. 

 Until comparatively recently it was thought that the proteases 

 were confined to the alimentary canal of animals. But since 

 1890, thanks to the researches of Salkowsky, Jacoby, Hedin, and 

 others, it has been gradually ascertained that a proteolytic enzyme 

 is to be found generally in the tissues ; an enzyme that resembles 

 trypsin in its digestive activity, but differs fi-om it in being more 

 active in acid (0-1 per cent. HCl) than in neutral or alkaline 

 liquids ; this protease may be distiugaished as " tissue-trypsin." 

 But the most recent and, from the present point of \'\e\\\ the 

 most interesting discovery in this direction is that made by A' ernon, 

 that an erepsin can be readily extracted from the various tissues 

 of both vertebrate and invertebrate animals. Though his paper 

 has not yet been publislied, I have the author's permission to make 

 brief mention of his results on this occasion. In the Mammalia 

 this " tissue-erepsin," as the protease may be designated, closely 

 resembles in its properties the intestinal erepsin, " entero-erepsin,'' 

 discovered by Cohuheim, more especially in requiring an alkaline 

 medium. But the investigation of certain lower Vertebrates 

 (Pigeon, Frog, Eel) and Invertebrates (Lobster, Anodou) has 

 shown that in the latter cases an acid medium is less prejudicial 

 than in the former to the action of the protease. These results 

 demonstrate not only the fact of the essential similaritj- of dis- 

 tribution of erepsin in the tissues of animals and of plants, but 

 also indicate a gradual convergence in the properties of the 

 erepsins ; so that it is not too much to anticipate the discovery of 

 animals possessing an erepsin which, like that of plants, is more 

 especially adapted for action in an acid medium. 



But I must return to the consideration of the nature of the 

 vegetable proteases, and more especially of the fibrin-digesting 

 proteases. In endeavouring to solve this problem, I have ascer- 

 tained that in certain cases (Yeast, Mushroom) the tissues contain 

 a mixture of erepsin with a fibrin-digesting enzyme, a result whicli 

 finds its analogue in Yernon's researches on pancreatic trypsin. 

 But I have not succeeded in determining the nature of this fibrin- 

 digesting enzyme, in deciding whether it is a pepsin or a trypsin, 

 because there is no method by which all the erepsin can be 

 certainly removed from the mixture so as to leave the other 

 enzyme isolated. 



However, I have recently made some observations in another 

 direction which, though not yet conclusive, at any rate indicate a 

 method by which a physiological analysis of a suspected mixture 

 of proteases may be attempted. In investigating the somewhat 

 debated digestive properties of papain, it was necessary, as in all 

 experiments of this kind, to use an antiseptic. I tried various 



