2 
Vines . — The Proteases of Plants (VI). 
stated that the milky juice of the fruit ‘ is of so penetrating a nature that 
if the unripe fruit, unpeeled, be boiled with the toughest old salt meat 
it will soon make it soft and tender ; and if hogs are for any considerable 
time fed with it, especially raw, it is said that it will wear off all the 
mucous slimy matter which covers the inside of the guts, and would in 
time, if not prevented by a change of food, entirely lacerate them A 
similar account was given by Patrick Browne in his £ Civil and Natural 
History of Jamaica’ (1J56). He says: 'Water impregnated with the 
milky juice of this tree is thought to make all sorts of meat washed in 
it very tender ; but eight or ten minutes’ steeping, it is said, will make it so 
soft that it will drop in pieces from the spit before it is well roasted, or 
turn soon to rags in the boiling.’ 
The latex was first investigated scientifically by Wurtz and Bouchut 
( 1 ). Having extracted the latex with distilled water, they mixed the 
aqueous extract with ten times its volume of alcohol : the considerable 
precipitate formed was collected in a filter and dried. To the white 
powder thus obtained they gave the name papain , and regarded it as the 
digestive enzyme of the latex. They observed that an aqueous solution 
(0-2 percent.) of this powder readily digested fibrin at 40 0 C., whether 
the liquid were neutral, slightly alkaline (KHO) or acid (0-2 per cent. 
HC 1 ). They found the ultimate products of the fibrin-digestions to be 
peptones. On this account they considered papain to be allied to animal 
pepsin, but to differ from it in that it digests in neutral, acid, and alkaline 
medium, whereas the action of pepsin is limited to an acid medium. 
Their ultimate view is expressed in the following words : — * II circule 
reellement dans les differentes parties de cet arbuste un sue presque neutre 
qui a toutes les proprietes de la pepsine , sauf que celle-ci est acide, et n’agit 
qu’etant acide ; et quelques proprietes de la pancreatine , ce qui en fait une 
sorte de pancreatine vegetalel 
After a considerable lapse of time, the investigation of papain was 
resumed by Martin ( 2 ). From the analysis of ‘ commercial papain ’, he 
came to the conclusion that papain consists of a mixture of two proteids, 
a globulin and an albumose, and that the ferment-action is associated with 
the albumose. Having proved the formation of leucin and tyrosin in the 
course of digestion of fibrin and albumin, Martin concluded ( 3 ) that papain 
is the only vegetable ferment which has as yet been proved to act like 
trypsin, and then its normal action takes place in a neutral medium. Thus 
it was shown that papain not only digests the higher proteins, but also 
hydrolyses the peptones : it both peptonizes and peptolyses. 
Several years after Martin’s papers had appeared, I made some ex- 
periments on papain-digestion ( 14 ), and found, by means of the tryptophane- 
test, that papain actively digests peptones in neutral solution, more actively 
in the presence of acid (best in 0-5 per cent, citric acid), and less actively in 
