252 VEGETABLE PHYSIOLOGY 
The members of the second group, which may be represented 
by the trypsin of the pancreas, carry the digestion further 
and split up certain peptones into amino- and amido-acids, 
of which the chief that have been observed are leucin, 
tyrosin, and asparagin. Those of the third class, the 
erepsins, decompose peptone with the formation of the same 
amino- and amido-acids. 
It is not quite certain that representatives of the first 
class are to be met with in plants. It is for the present 
probable, however, that the enzyme of some insectivorous 
plants is a pepsin. It acts only in the presence of a weak 
acid, as does the pepsin of the stomach, but the products 
which it forms have not been accurately investigated. It 
is apparently only secreted when the gland has been 
stimulated by the absorption of nitrogenous matter. 
Several varieties of vegetable trypsin have been dis- 
covered and their properties investigated. The earliest 
known enzyme belonging to the group is the papain which 
has been extracted from the Papau (Carica Papaya). It 
appears to exist in greatest quantity in the pulp of the 
fruit, but is present also in the sap which can be expressed 
from the stem and leaves. It is apparently associated in 
the juice with a peculiar proteose or albumose, and it is 
most energetic in a neutral solution, though it can act 
also in a faintly alkaline one. It is easily destroyed by a 
very small trace of free acid. 
Another trypsin, which has been named bromelin, has 
been extracted from the fleshy pulp of the Pine-apple 
(dnanassa sativa). Like papain it is associated with a 
proteose. It acts most energetically in neutral and faintly 
acid solutions, alkalies in very small traces being preju- 
dicial to it. Its activity varies a good deal according to 
the acid which is present, and to some extent according to the 
protein which it is digesting. 
Other vegetable trypsins have been extracted from the 
germinating seeds of the Lupin, the seedlings of several 
plants, the fruit of the Kachree gourd (Cucumis utilissimus), 
