[Illustration: Fig. 86. A secretory follicle. An artery is seen, which supplies the material for its secretion. Follicles are also supplied with veins and organic nerves.] 417. The FOLLICLES are small bags, or sacs, situated in the true skin, and mucous membrane. The pores seen on the skin are the outlets of these bodies. -=-=-=-=-=-=-=-=-=-=-=-= 414. How are the fluids and solids of the body produced? 415-419. _Give the anatomy of the secretory organs._ 415. Name the secretory organs. 416. Describe the exhalants. What is represented by fig. 86? 417. Define follicles. -=-=-=-=-=-=-=-=-=-=-=-= 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. -=-=-=-=-=-=-=-=-=-=-=-= 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? -=-=-=-=-=-=-=-=-=-=-=-= 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 woody fibre. All are composed of the same few, simple elements, arranged in different order and proportions."