DIGESTION 251 
There appear to be several varieties of cytase, which 
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. proteis are frequently on 
that account spoken of as proteoclastic enzymes. There are 
three 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 
proteins into peptones, several intermediate bodies, known 
as proteoses or albumoses, being formed during the process. 
