32 CEREALS 
oxygen in nearly the same proportions,—the composition 
of starch being carbon, six parts; hydrogen, ten; and oxygen, 
five; as expressed by the formula C,H,.O;; while for pure 
glucose the formula is C,H,,0,. It will be noticed that 
in each there is twice as much hydrogen as oxygen; that is 
to say these elements are present in just the same,propor- 
tion as in water, which, as is well known, has the chemical 
formula H,O. <A substance which is thus composed of car- 
bon united with the elements of water is called a carbohy- 
drate.. Not only do starch and glucose come under this 
head, but also other kinds of sugar, various sorts of true gum 
(such for example as that on postage stamps), and the sub- 
stance known as cellulose of which wood, cotton, and paper 
are mainly composed. Among the cereal grains, although 
sugar is sometimes present to a notable degree, as in “‘sweet 
corn,” the amount of digestible carbohydrate as given in the 
tables may be understood as being almost entirely starch. 
During the process of digestion in man and other animals 
starch is converted into sugar, and as such is absorbed into 
the blood and carried all over the system to serve either 
for making fat or for giving warmth and strength. Since 
only fluids can be absorbed, and since starch is composed of 
solid insoluble particles, the necessity of somehow converting 
the starch of our food into sugar, is obvious. 
Similarly, when grains sprout, the starch in them under- . 
goes a sort of digestion and becomes converted into sugar, 
largely maltose or ‘malt sugar” (formula C,,H..O,,). This 
being soluble in the sap of the young plant, may be car- 
ried to the regions of growth where food is needed. ‘This 
change of the insoluble starch into the soluble sugar is 
accomplished through the action of a substance called 
diastase, one of a remarkable class of substances known as 
enzymes 2 that have the power of bringing about such changes — 
by their presence in comparatively minute amount. The 
process of malting consists in causing grain to sprout and 
allowing the conversion of starch to proceed until as much 
' Car-bo-hy’drate < L. carbo, coal; Gr. hydor, water. ‘ote 
2 En/zyme < Gr. en, in; zyme, leaven; so called because acting like 
the substance in leaven or yeast which produces similar changes. 
