ive the anatomy of the secretory organs._ 415. Name the secretory
organs. 416. Describe the exhalants. What is represented by fig. 86?
417. Define follicles.

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418. The GLANDS are soft, fleshy organs, and as various in their
structure, as the secretions which it is their function to produce.
Each gland is composed of many small lobules united in a compact mass,
and each lobule communicates by a small duct with the principal
outlet, or duct of the organ. Every gland is supplied with arteries,
veins, lymphatics, and nerves. These, with the ducts, are arranged in
a peculiar manner, and connected by cellular membrane.

419. There are two classes of glands, one for the modification of the
fluids which pass through them, as the mesenteric and lymphatic
glands; and the other for the secretion of fluids which are either
useful in the animal economy, or require to be rejected from the
body.

[Illustration: Fig. 87. 1, 1, A secretory gland. 2, 2, Minute ducts that
are spread through the glands. These coalesce to form the main duct, 3.]

PHYSIOLOGY OF THE SECRETORY ORGANS.

420. SECRETION is one of the most obscure and mysterious functions of
the animal economy. "It is that process by which various substances
are separated from the blood, either with or without experiencing any
change during their separation." Not only is the process by which
substances are separated from the blood, called secretion, but the
same term is also applied to substances thus separated. Thus
physiologists say, that by the process of secretion, bile is formed by
the liver; and also, that bile is the secretion of this organ.

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418. Give the structure of the glands. 419. How are the glands
arranged? 420-431. _Give the physiology of the secretory organs._ 420.
What is secretion?

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421. The secreted fluids do not exist in that form in the blood,
but most of the elements of which they are made do exist in this
fluid, and the "vessels by which it is accomplished may well be called
the architects and chemists of the system; for out of the same
material--the blood--they construct a variety of wonderful fabrics
and chemical compounds. We see the same wonderful power possessed,
also, by vegetables; for out of the same materials the olive prepares
its oil, the cocoa-nut its milk, the cane its sugar, the poppy its
narcotic, the oak its green pulpy leaves, and its dense woo