one
it can be assimilated. This conversion is carried out by the saliva.
Hence the necessity for thorough mastication, even of sloppy foods that
do not seem to require it, and for attention to the teeth in order that
they may thoroughly chew. Alcohol and tobacco, as they spoil the
saliva, are very unfavourable to digestion, and should always be
avoided. Twenty minutes longer to chew one's dinner is worth a whole
box of pills, and no one need expect good digestion who neglects
thorough chewing and salivation of the food. This may, with advantage,
be increased to an extent which most people would think quite absurd.
It has been proved that when all food is chewed until completely
reduced to a liquid, its nutritive qualities are so increased that
about half as much will suffice. This is of immense importance in all
cases of weak digestion, or indeed whenever an absence of vigorous
health renders the economy of vital energy important.

[Illustration: Digestive System.]

In the stomach the food meets with the gastric juice, which has the
property of turning proteid (_see_ Diet for the various substances
contained in food) into material ready for assimilation. The walls of
the stomach are muscular, and their contraction churns the food with
the juice. The gastric juice is secreted by glands embedded in the
walls of the stomach, and is poured out when food is taken.

The whole food, now in the form of a paste, passes into a pipe about 12
inches long (the Duodenum), into which pours the secretion of the
pancreas and that of the liver (bile). The pancreatic juice acts upon
the starch which has escaped the action of the saliva, and also
continues the work of the stomach. It furthermore emulsifies the fat or
divides it into extremely fine drops.

The food passes now into a long coiled pipe--the small intestine. This
secretes the intestinal juice which further assists the pancreatic
juice. Absorption has been proceeding from the stomach onwards (_see_
Assimilation). The mass of undigested food is pushed along the small
intestine by means of muscles in its walls and passes into the large
intestine where a similar process to that of the small intestine goes
on, the remains of the food ultimately reaching the vent in a semi
solid form, consisting of the undigested part and the debris of
digestion.

During this complex process much blood and energy is needed for the
abdominal region, therefore hard work or exercise should not
im