DIGESTION 265 



can be prepared from various seeds. The enzyme was 

 first discovered in the germinating grain of the barley, in 

 which it is located chiefly in the aleurone layer and to a 

 less extent in the epithelium of the scutellum, where it 

 exists side by side with diastase. It dissolves the walls of 

 the cells of the endosperm, detaching them from each other 

 and giving a curious mealy character to the grain. Its 

 presence was first suspected in the Date-palm, where large 

 reserves of cellulose are found in the hard cell-walls of the 

 endosperm. The embryo dissolves these walls and absorbs 

 their products, the work being effected by an epithelium 

 which covers the part of the cotyledon which remains in 

 the seed during the early processes of germination. This 

 epithelium is composed of elongated cells arranged in a 

 manner resembling that characteristic of those which form 

 the secreting layer of the scutellum. It has recently been 

 shown that cytase is formed in the embryo, probably in this 

 layer, and passes thence into the endosperm. The amount 

 of it that can be detected is very small, however, and the 

 process of the decomposition of the cellulose is very slow 

 and gradual. Cytase exists in considerable quantity in 

 some of the higher fungi and in certain bacteria. 



Pectase has recently been found to be very widespread 

 in plants. Its function is not very clear, but it may assist 

 cytase in the swelling up of the cell-wall which is ante- 

 cedent to solution. It is recognised by its power of forming 

 vegetable jelly from the pectic substances of the cell-wall. 

 This jelly appears to be a compound of pectic acid and 

 calcium. 



The enzymes which digest proteids are frequently on 

 that account spoken of as proteolytic enzymes. There are 

 two main classes of them known at present. The first, 

 represented by the pepsin of the stomach of the higher 

 animals, converts albumins, globulins, and certain insoluble 

 proteids into peptones, several intermediate bodies, known 

 as proteoses or albumoses, being formed during the process. 

 The second group, which may be represented by the 



