y.

~Disaccharides.~--Of the second group of carbohydrates, we are
probably more familiar with sucrose, or cane sugar, than with either
of the other two, since it is in this form that the greater part of
the sugar eaten is purchased.

~Sucrose.~--By far the greater part of the sugar entering into the
average dietary is manufactured from sugar and sorghum canes, and from
sugar beets; but appreciable quantities are derived from the sugar
maple and sugar palms. Many of the sweet fruits are rich in this form
of sugar; pineapples are said to contain at least half of their solids
in sucrose; and although other fruits and vegetables do not contain so
high a percentage of this sugar, oranges, peaches, apricots, dates,
raisins, prunes, carrots and sweet potatoes contain goodly quantities,
which are associated with glucose and fructose. Sucrose is readily
hydrolized, either by acids or enzymes. The inverting enzyme
(invertase) of yeast and sucrase of the intestinal juice, convert
sucrose to fructose and glucose, in which forms it is absorbed into
the portal blood. It is believed that when sucrose is eaten in very
large quantities, it is sometimes absorbed from the stomach. In these
cases it does not become available for use in the body, but acts in
the same manner as when injected directly into the blood stream, being
excreted unchanged by way of the kidneys. According to Herter, sucrose
is much more susceptible to fermentation in the stomach than either
maltose or lactose; and since it has no advantage over these sugars
from a standpoint of nutrition, they are frequently substituted for
sucrose in cases where the dangers arising from fermentation must be
avoided.

~Maltose~ (Malt sugar) is an important constituent of germinating
grains--malt and malt products being formed as the result of enzymic
action (amylases) on starch. A similar action takes place in the mouth
as the result of the ptyalin in the salivary juices and in the
intestines from the action of the starch-splitting enzyme, amylopsin,
in the pancreatic juice. The maltose thus formed is further converted
into glucose by the sugar-splitting enzyme in the intestinal juice,
and in this form it is chiefly absorbed. Maltose is also an
intermediate product formed during the manufacture of commercial
glucose as the result of the boiling of starch with dilute acids.

~Lactose~ (sugar of milk) is one of the most important constituents in
the milk of all mammals. In freshl