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 papam 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 

 (Ananassa saliva). 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), 



