LINNEAN SOCIETY OF LONBOX. 2 1 



nimjerous experiments made with various plants and parts of 

 plants in which I have detected digestive action, that the enzymes 

 act proteolytically. In view of this accumulating evidence, the 

 only possible conclusion to be drawn is that the proteases of 

 plants are essentially proteolytic : there is, in fact, no record 

 of the existence in any plant of a merely or mainly peptonising 

 enzyme. 



This conclusion has not been arrived at without contradiction. 

 In the case of the pitcher-plant Nepenthes, the lafe Dr. Clautriau 

 contested the accuracy of my results, asserting that here was 

 an instance of simple peptonisation. However, I have never 

 failed to obtain evidence of proteolysis in digestiA-e experiments 

 with the pitcher-liquid, and can only suggest that the conditions 

 of Dr. Clautriau's experiments were in some way unsuitable, 

 probably because the necessary acid was not supplied. More 

 recently Dr. Mendel has asserted that papain can peptonise but 

 not proteolyse the higher proteids. tn a paper which is shortly 

 to be published, I have shown, I think conclusively, that the 

 cause of the divergence between Dr. Mendel's results and my own 

 is that the antiseptic which he used in his experiments interfered 

 with the action of the enzyme. 



I may now very briefly describe the methods which I have 

 adopted for the purpose, (1) of detecting the presence of a 

 protease, and (2) of determining the nature of its action. 



In the first instance, the method employed was the usual one 

 of submitting some blood-fibrin to the action of the liquid, with 

 due antiseptic precautions, and observing the more or less 

 complete solution of it in the course of the experiment. It was 

 in this way that the digestive activity of Nepenthes-\\C[\x\d, Papaw, 

 of Pineapple-juice, and of solutions of papain, had been first 

 discovered ; and it Mas in this ^ay that I detected it in the Yeast, 

 the Mushroom, the Melon, and other plants. But in many 

 cases the result was altogether negative, and for the moment 

 I followed the usual course of accepting this as evidence for the 

 total absence of digestive power in these cases. 



Confining my attention to the positive results, I endeavoured to 

 ascertain, by an examination of the products of digestion, what 

 had been the action of the protease in each case, whether merely 

 peptonising or completely proteolytic. In devising a simple 

 method for doing this, I remembered that one of the constant 

 products of pancreatic digestion is a substance termed tryptophane, 

 which gives a pink or violet colour on the addition of chlorine- 

 water. As the presence of tryptophane is accepted as evidence 

 of proteolysis effected by trypsin, it would also be evidence of 

 proteolysis by vegetable proteases. I accordingly tested the 

 liquids resulting from fibrin-digestions with the various plant- 

 materials just mentioned, and in every case there was unmistak- 

 able evidence of the presence of tryptophane. The conclusion is 

 therefore inevitable, that in all these cases the enzyme is, like 

 trypsin, capable not only of peptonisation but also of proteolysis. 



