Chapter IV — 71 — Nepenthes 



with 1% acetic acid for 24 hours, before extracting with glycerin, and 

 found that this extract was more powerful than that of the control 

 prepared without previous acid treatment. This indicated that, as in 

 the case of animal glands (Haidenhain) , the ferment exists in the 

 glands as a zymogen, a basic substance from which the ferment is 

 derived by acidification. The facts seemed to bring the whole phe- 

 nomenon of plant digestion into line with that in animals. This was 

 the beginning of a sustained investigation on the part of Vines on this 

 subject. Dubois and Tischutkin held that there is no digestion 

 proper to the Nepenthes pitcher, and that such digestion as takes place 

 is bacterial. Goebel's examination of the matter, however, afforded 

 experimental evidence in agreement with that of Vines (1877), who 

 now, however, repeated and extended his earlier work and drew the 

 conclusion that settled the matter to all appearances. For instance, 

 he showed that digestion goes on in the fluid of (unopened) pitchers 

 in the presence of poisons deadly to bacteria (HCN, thymol, KCN, 

 chloroform); but as opened pitchers were used the possibility is not 

 excluded that a bacterial ferment had already accumulated. Vines 

 concluded that the ferment present in the pitchers is secreted by the 

 pitcher glands, is not a product of bacteria, but is tryptic in na- 

 ture, like that of certain seeds (Green 1899) not producing pep- 

 tones, or if it does, these are broken down at once into other bodies 

 (leucine, etc.). It is remarkably stable and has an antiseptic action. 

 The pitcher liquid is usually distinctly acid, contrary to the prevaihng 

 views, the acidity therefore not depending on the supposed stimula- 

 tion by foreign bodies. In his third paper (1898) Vines showed more 

 in detail that the enzyme is unusually stable towards heat and alkalis, 

 for while exposure to these agencies does reduce its activity, "it re- 

 tains a sort of residual digestive power which asserts itself in a very 

 slow and prolonged digestion, and which can only be destroyed by 

 very strong measures." The enzyme exists in the tissues as a zymo- 

 gen, is essentially tryptic in character, and among its products of di- 

 gestion true peptones are present. In his last paper published in 1901, 

 Vines proposed the name "nepenthin" for the proteolytic ferment 

 which he had previously studied and made further tests of the action 

 of the pitcher fluid on fibrin and on Witte peptone, exposing them to 

 action for several days at 38.5 degrees C. with the addition of HCl 

 or citric acid. The results showed the presence of tryptophane, char- 

 acteristic of tryptic digestion. 



The detail of Vines' general conclusions, that the digestion is 

 rather of the tryptic kind, was later called in question by Abderhalden 

 and Teruuchi (1906). From data obtained by experiments in which 

 glycyl-1-tyrosin was used, which gave negative results, they concluded 

 that the Nepenthes protease is not a trypsin, though they did not as- 

 sert certainty in view of the lack of sufficient material for further work 

 {See Stern and Stern, beyond). 



Quite opposite conclusions were drawn by Tischutkin (1891), 

 Dubois (1890) and Couvreur (1900). Tischutkin placed small cubes 

 of egg-albumin in unopened pitchers by passing them through a small 

 window cut in the wall under sterile conditions, and saw no digestion. 

 When the test material was placed in pitcher fluid in vitro, digestion 



