Troussart's
_Microbes, Ferments, and Moulds_.

[19] "The physiological wear of the organism is constantly being repaired
by the blood; but in order to keep the great nutritive fluid from becoming
impoverished, the matters which it is constantly losing must be supplied
from some source out of the body, and this necessitates the ingestion of
articles which are known as food."--Flint's _Text-book of Human
Physiology_.

[20] Glands. Glands are organs of various shapes and sizes, whose
special work it is to separate materials from the blood for further use in
the body, the products being known as secretion and excretion.
The means by which secretion and excretion are effected are, however,
identical. The essential parts of a gland consist of a basement membrane,
on one side of which are found actively growing cells, on the other is the
blood current, flowing in exceedingly thin-walled vessels known as the
capillaries. The cells are able to select from the blood whatever material
they require and which they elaborate into the particular secretion. In
Fig. 47 is illustrated, diagrammatically, the structure of a few typical
secreting glands. The continuous line represents the basement membrane.
The dotted line represents the position of the cells on one side of the
basement membrane. The irregular lines show the position of the
blood-vessels.

[21] Tablets and other material for Fehling and additional tests for sugar
can be purchased at a drug store. The practical details of these and other
tests which assume some knowledge of chemistry, should be learned from
some manual on the subject.

[22] The Peritoneum. The intestines do not lie in a loose mass in the
abdominal cavity. Lining the walls of this cavity, just as in a general
way, a paper lines the walls of a room, is a delicate serous membrane,
called the peritoneum. It envelops, in a greater or less degree, all
the viscera in the cavity and forms folds by which they are connected with
each other, or are attached to the posterior wall. Its arrangement is
therefore very complicated. When the peritoneum comes in contact with the
large intestine, it passes over it just as the paper of a room would pass
over a gas pipe which ran along the surface of the wall, and in passing
over it binds it down to the wall of the cavity. The small intestines are
suspended from the back wall of the cavity by a double fold of the
peritoneum, called the mesentery. The bowels are also protected