mposes one-half of peas, beans, wheat,
oats and rye, three-fourths of corn and rice, one-fifth of potatoes.
Vegetable proteids, as already stated, are less easily digested than
those belonging to the animal kingdom, therefore it must be remembered
that a purely vegetable diet, even though it may be so arranged as to
provide the necessary protein, is apt to over-tax the digestive
organs more than a mixed diet from both the animal and vegetable
kingdoms. Much depends upon the cooking of the starchy foods in order
to render them digestible. (Study chapter on Digestion in the Public
School Physiology.)

STARCH.

The digestion of starch--which is insoluble in cold water--really
begins with the cooking, which by softening the outer coating or fibre
of the grains, causes them to swell and burst, thereby preparing them
for the chemical change which is caused by the action of the saliva in
converting the starch into a species of sugar before it enters the
stomach. Substances which are insoluble in cold water cannot be
absorbed into the blood, therefore are not of any value as food until
they have become changed, and made soluble, which overtaxes the
digestive organs and causes trouble. The temperature of the saliva is
too low to dissolve the starch fibre unaided. Each of the digestive
juices has its own work to do, and the saliva acts directly upon the
starchy food; hence the importance of thoroughly masticating such food
as bread, potatoes, rice, cereals, etc. The action of heat, in baking,
which causes the vapor to rise, and forms the crust of starchy food,
produces what is called dextrine, or partially digested starch.
Dextrine is soluble in cold water, hence the ease with which crust and
toast--when properly made--are digested. It is more important to
thoroughly chew starchy food than meat, as it is mixed with another
digestive juice, which acts upon it in the stomach.

Sugars.

SUGAR.

There are many varieties of sugar in common use, viz.: cane sugar,
grape sugar or glucose, and sugar of milk (lactose). As food, sugars
have practically the same use as starch; sugar, owing to its
solubility, taxes the digestive organs very little. Over-indulgence in
sugar, however, tends to cause various disorders of assimilation and
nutrition. Sugar is also very fattening, it is a force producer, and
can be used with greater safety by those engaged in active muscular
work. Cane sugar is the clarified and crystallized juice of the s