The magnification is too low to show the smaller blood vessels.5.One of the glands alongside of the hair which furnishes an oily secretion.6.A sweat gland.7.The fat of the skin.

Notice that hair, hair glands and sweat glands are continuous with the surface and represent a downward extension of this.

All the tissue below 2 and 3 is the corium from which leather is made.] [Illustration: FIG.

4 .-- DIAGRAMMATIC SECTION OF A SURFACE SHOWING THE RELATION OF GLANDS TO THE SURFACE.

(_a_) Simple or tubular gland, (_b_) compound or racemose gland.] All of the causes of disease act on the body from without, and it is important to understand the relations which the body of a highly developed organism such as man has with the world external to him.
This relation is effected by means of the various surfaces of the body.