mouth, and the parotid, the submaxillary, and the sublingual glands. The
process of its secretion is constant, but is greatly augmented by the
contact of food with the lining membrane. The saliva serves to moisten
the triturated food, facilitate its passage, and has the property of
converting starch into sugar; but the latter quality is counteracted by
the action of the gastric juice of the stomach.

GASTRIC JUICE. The minute tubes, or follicles, situated in the mucous
membrane of the stomach, secrete a colorless, acid liquid, termed the
gastric juice. This fluid appears to consist of little more than water,
containing a few saline matters in solution, and a small quantity of
free hydrochloric acid, which gives it an acid reaction. In addition to
these, however, it contains a small quantity of a peculiar organic
substance, termed _pepsin_, which in chemical composition, is very
similar to ptyalin, although it is very different in its effects. When
food is introduced into the stomach, the peristaltic contractions of
that organ roll it about, and mingle it with the gastric juice, which
disintegrates the connective tissue, and converts the albuminous
portions into the substance called chyme, which is about the consistency
of pea-soup, and which is readily absorbed through the animal membranes
into the blood of the delicate and numerous vessels of the stomach,
whence it is conveyed to the portal vein and to the liver. The secretion
of the gastric juice is influenced by nervous conditions. Excess of joy
or grief effectually retard or even arrest its flow.

INTESTINAL JUICE. In the small intestine, a secretion is found which is
termed the _intestinal juice_. It is the product of two classes of
glands situated in the mucous membrane, and termed respectively, the
_follicles of Lieberkuhn_ and the _glands of Brunner_. The former
consist of numerous small tubes, lined with epithelium, which secrete by