A small glandular organ at the base of the brain, the pituitary body, produces a secretion, one of the most marked properties of which is a control of growth, particularly that of the bones.

Most cases of giantism, combined as they are with imperfect mentality, are due to disease of this gland.
There are glands near the kidney which regulate the pressure of the blood in the arteries by causing contraction of their muscular walls.
The sexual characteristics in the male and female are due to an internal secretion produced by the respective sexual glands which affects growth, body development and mentality.
So is the body constituted.

A series of surfaces, all connected, of enormous size, which enclose a large number of organs and tissues, the activities of which differ, but all are cooerdinated to serve the purposes of the organism as a whole.

We should think of the body not as an assemblage of more or less independent entities, but as a single organism in which all parts are firmly knit together both in structure and in function, as are the components of a single cell.
FOOTNOTES: [1] They do, however, take place, since within comparatively few years whole species have completely disappeared; for example, the great auk and the passenger pigeon.

In these cases it is not known what part disease played in the destruction.
[2] A tissue represents an aggregate of similar cells with the intercellular substances in relation with these as connective tissue, muscular tissue, etc.