Vines.— The Proteases of Plants (VI). n 
pancreatin (i. e. trypsin). Martin’s investigation of papain carried the 
matter a good deal further on in the same direction. He found leucin and 
tyrosin among the products of digestion, and ascertained that the presence 
of acid retarded, whilst that of alkali, within certain limits, accelerated, 
digestion ; consequently he associated it, though very cautiously, with 
animal trypsin. 
In this way the second general idea, what may be termed the trypsin - 
idea , of plant-proteases originated, the idea that these proteases not only 
peptonize fibrin and other proteins, but further split up the albumoses and 
peptones into amino-acids, such as leucin and tyrosin, and other nitrogenous 
substances. It was soon supported by a considerable amount of experi- 
mental evidence. Thus, Green found that from germinating seeds (Lupin, 
Castor-oil) extracts could be obtained which digested fibrin, in the presence 
of o-2 per cent. HC 1 , leucin, tyrosin, and asparagin being formed during 
digestion (6, 7). Soon afterwards he showed that the Kachree Gourd (Cu- 
cumis Melo var. utilissimus ) contains an enzyme which digested coagulated 
egg-albumen actively in alkaline (1-5 per cent. Na 2 C 0 3 ) medium, less 
actively in neutral, and least actively in acid (0-2 per cent. HC1) ; he found 
leucin among the products of digestion (8). Hansen’s observations on the 
latex of the Fig ( Ficus Caricd) may be mentioned, though they are in- 
conclusive ( 9 ). The latex digested fibrin in both acid (0-2 per cent. HC 1 ) 
and alkaline (2 per cent. Na 2 C 0 3 ) medium ; the products of digestion were 
not fully examined, but leucin and tyrosin were not found in the alkaline 
digestion. Chittenden (10), investigating the juice of the Pine-apple (Ananas 
sativus ), observed that it digested fibrin most actively at its own natural 
acidity, and that leucin and tyrosin were products of digestion. He also 
found that the juice digested coagulated egg-albumen most actively when 
neutral in reaction, less actively at natural acidity, or at an alkalinity of o-i 
per cent. Na 2 C 0 3 , still less actively when made more alkaline or more acid 
(with HC1), and that digestion was arrested by an alkalinity =1 per 
cent. Na 2 C 0 3 , and (in an artificial solution) by an acidity = o«i per cent. 
HCL 
Further evidence of this kind was afforded by my observations upon 
the digestive properties of the pitcher-liquid of Nepenthes (11, 12, 13 , 1897-8, 
1901). In these three papers I showed that the liquid has a ‘ tryptic ’ 
action, inasmuch as it not only peptonizes fibrin, but also splits the peptones 
into amino-acids, such as leucin and tryptophane. It was in the last of these 
three papers that I introduced the chlorine-reaction for tryptophane into the 
study of the proteolysis of plants. Although digestion was found to take 
place only in acid medium, I considered that the enzyme of the pitcher- 
liquid should be regarded as belonging to the trypsin-group (tryptases), 
on account of the products formed in digestion ; and in the last of the three 
papers I went so far as to express the opinion ‘ that all known proteolytic 
