258 VEGETABLE PHYSIOLOGY 



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 peptase. 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 stimu- 

 lated by the absorption of nitrogenous matter. 



Several varieties of vegetable tryptase 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 tryptase, which has been named bromelin, has 

 been extracted from the fleshy pulp of the Pine-apple 

 (Ananassa 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 tryptases have been extracted from the 

 germinating seeds of the Lupin, the seedlings of several 

 plants, the fruit of the Kachree gourd (Cucumis utilissimus), 

 the juice of the Fig-tree (Ficus carica), and the leaves of 

 certain species of Agave. How far these are identical, or 

 whether they present specific differences, appears at present 

 uncertain. They are all active in faintly acid solutions, 

 but the most favourable concentration appears to vary. 

 The enzyme of the Kachree gourd is most effective when 

 the medium is faintly alkaline, whereas that of the lupin 



