ACTIC ACID is common to all the solids and fluids of the system. It
is found united with potash, soda, lime, or magnesia.

D.

The word _duodenum_ is derived from the Latin, signifying "twelve,"
since the intestine, of which this is the name, is usually about
twelve fingers' breadth in length. The _jejunum_ is also from the
Latin _jejunum_, empty, since it is usually found in that condition
after death, as the food seems to pass rapidly through this part of
the intestine. The term _ileum_ is from the Greek, signifying "to
twist," since it always appears in a contorted condition. The name
_caecum_ is derived from the fact of its being a blind or short sack,
perforated by the extremity of the ileum. The name of the next
division of the intestine--_colon_--is from the Greek, "to prohibit,"
as the contents of the alimentary canal pass slowly through this
portion. The _rectum_ is named from the straight direction that it
assumes in the latter part of its course.

E.

The food is forced through the alimentary canal by contractions of its
muscular coat, produced by the nervous filaments of the sympathetic
system, not being at all dependent on the cerebro-spinal centre. This
is called the peristaltic, or vermicular motion. The great length of
intestine in all animals, and especially in the herbivorous ones, is
owing to the necessity of exposing the food to a large number of the
lacteals, that the nourishment may all be taken from it.

F.

The different processes through which the food passes before
assimilation are of considerable interest. The mastication and mixture
of the saliva with the food are purely of a mechanical nature. When
any solid or fluid substance is placed upon the tongue, or in contact
with the inner surface of the cheeks, by an involuntary act, the
salivary glands are stimulated to activity, and commence pouring the
saliva into the mouth through the salivary ducts. As soon as
mastication commences, the contraction of the masseter and other
muscles employed in mastication stimulates the salivary glands to
increased action, and a still greater quantity of saliva is secreted
and forced upon the food, which is constantly being ground to a finer
condition, until it is sufficiently reduced for deglutition.

Whether the salivary fluid acts any other part than simply that of a
demulcent to assist the gastric juice in still further dissolving the
food, is yet a matter of some doubt, although it is found