ENZYMES AND THEIE ACTION 457 



besides many bacteria. Its action is the hydrolysis of cane- 

 sugar witli the formation of dextrose and levulose, according to 

 the equation 



C„H,,Ojj + H,0 = C,Hi,0, + CgHioO, 



Cane-sugar. Dextrose. Lerulose. 



Glucase occurs in the seed of the Maize. It converts 

 maltose into dextrose. 



Cytase is chiefly known in the germinating grain of the 

 barley, where it is secreted by the seutellum together with the 

 diastase. It dissolves the walls of the cells of the endosperm, 

 setting them free and giving a ciirious mealy character to the 

 grain. Its presence is suspected in the Palms, where large 

 reserves of cellulose are found in the hard endosperm walls. 

 The embryo dissolves these walls and absorbs their products, 

 but whether the ferment has a free existence is not yet settled. 

 Cytase abounds in certain. Fungi belonging to the genus 

 Botrytis. 



Peotase is but little known, and its function is not very clear. 

 It is recognised by its power of forming vegetable jelly from the 

 peetic bodies of the cell-wall. This jeUy appears to be a com- 

 pound of peetic acid with calcium. 



The proteolytic enzymes pepsin and trypsin appear both to 

 be represented in plants, though to what extent the former exists 

 is somewhat uncertain. It is the enzyme which is found in the 

 insectivorous plants Drosera, Dionma, and others, and it con- 

 verts the native proteids of the insect's body into peptoiies, which 

 are absorbed by the leaf. It only acts in the presence of a weak 

 acid and is only formed by the plant when the gland has been 

 stimulated by the absorption of nitrogenous matter. Trypsin 

 has a much wider distribution, being known to exist in the fruits 

 of the Papau {Carica Papaya), the Eig, a variety of the Melon 

 [Oucumis utilissimus), and the Pine-apple {Ananassa sativa), 

 also in many seeds, such as those of the Hemp, Elax, Barley, 

 and Lupin. In the latter structures it is of especial value in the 

 processes of germination, feeding the young seedling with nutri- 

 tive proteid or nitrogenous matter until the time when it is able 

 to begin the constructive processes. 



It acts upon insoluble proteids, forming from them albumoses, 

 peptones, and amides, such as leucin, tyrosin, and asparagin. 

 The medium in which it works varies according to the source 

 of the enzyme ; that prepared from the Papau requires a slightly 

 alkaline one, that from the Lupin works best in a weak acid. 



