has a similar
action. To this, of which the exact chemical make-up is as yet an
unknown, they gave the name secretin.

Secretin and its properties they used to generalize as a perfectly
direct and amply demonstrable example of an internal secretion.
Metaphors are no less valuable in physiology than in poetry. They
declared that the internal secretions appeared to them to be chemical
messengers, telegraph boys sent from one organ to another through the
public highways, the blood (really more like a moving platform). So
they christened them all hormones, deriving the word from the Greek
verb meaning to rouse or set in motion. As a science is a well-made
language, a new word is an event. It sums up details, economizes
brain-work and so is cherished by the intellect. The study of the
internal secretions has advanced by leaps and bounds since it became
convenient to speak of them as hormones. Withal, the brilliant work of
Bayliss and Starling stands as the third great foundation stone,
the first Claude Bernard's and the second Brown-Sequard's, in the
architecture of the modern concepts of the internal secretions.

CHAPTER II

THE GLANDS: THYROID AND PITUITARY

The glands of internal secretion, the history of which, as tools of
thought, I reviewed in the previous chapter, have each an interesting
evolutionary story. Without some acquaintance with that story, the
rough outline of their physical architecture, and the particular work
they are called upon to perform in the body, no adequate understanding
of their influence upon types of human nature and personality is
possible.

THE THYROID GLAND

This gland consists of two maroon colored masses astride the neck,
above the windpipe, close to the larynx. These are bridged by a narrow
isthmus of the same tissue. They remind one of the flaps of a purse
opened up. The gland has always attracted much attention because its
enlargement constitutes the prominent deformity known as goitre.

To begin with, the thyroid was once a sex gland, pure and simple. In
the lowest vertebrates and in the homologous tissues of the higher
invertebrates, the fractions of the thyroid are intimately connected
with the ducts of the sexual organs. They are indeed accessory sexual
organs, uterine glands, satellites of the sex process. From Petromyzon
upward that relationship is lost, the thyroid migrates more and more
to the head region, to become the great link between sex and brain.
How a