The Organs of Secretion.

THE exhalants, the follicles, and the glands are the organs of secretion. The Exhalants are the sweatglands. These have external terminations upon the skin, thus communicating with the air, and internal terminations upon the surfaces of organs not having an outward exposure.

The Follicles are small sacs, located in the true skin and mucous membranes. The pores of the skin are the mouths or outlets of these little bags. Veins and organic nerves are sent to these vessels.

Glands are soft organs, having a variety of structure, and performing many kinds of secretion. A gland is made up of several lobules, united in one mass, and each of these lobules has a small duct, communicating with a main duct which forms the outlet. Fig. 39 shows a gland ; 2, the small ducts spread through its body, and running together; 1, the large duct, through which the secreted substance is carried away.

The mesenteric and lymphatic glands merely modify the fluids which pass through them; others secrete from the blood either fluids to be used in the body, or such as are to be cast away.