ernal secretion_ is a secretion formed by a gland, to be poured
into the blood or lymph system, while an _external secretion_ is
poured out through ducts to the exterior. The thyroid and adrenal
glands form internal secretions only, which secretions, poured into
the blood and lymph, profoundly affect the nutrition of the body. The
salivary glands and gastric glands form external secretions only;
which, when poured upon the food, digest it. The liver, pancreas and
testes form both external and internal secretions. The external
secretion of the testes is that which is poured out in a sexual
emission, as described above; the internal secretion of the testes
consists of substances formed by the testes of sexually mature
individuals, which substances, poured into the blood, profoundly
affect the development of the individual and his whole physical and
psychical character.

VIRILITY.

The best example that can be cited of the effect of this internal
secretion is the male of the horse kind.

Most young men have seen either at horse shows or upon farms or
ranches pedigreed stallions. No person can see one of these splendid
animals without admiring, if not actually standing in awe of his
inimitable physical force, beauty of form and grace and power of
action. He is a physical ideal of the horse kind. What is the source
of his strength and beauty?

The physical features that one notes peculiar to the stallion are,
first, the great breadth and depth of chest, great mass of shoulder
and hip muscles, and the high arched neck, fiery eye and luxuriant
mane and tail. Second, the functional features next noticeable are
the greater alertness and evident physical exuberance as manifested
especially in the gait and the frequent whinnying. The thoughtful
observer at the horse show or on the ranch cannot but compare these
animals with the gelding.

Two colts on the ranch may be full brothers,--from the same pedigreed
stallion and the same pedigreed dam. At the age of two years these two
young horses may be as alike as two peas in a pod. One of these
promising young animals is chosen, because of some commendable
peculiarity of temperament or action, to remain unmutilated, as a
procreator of his kind upon the ranch. The other is subjected to the
veterinarian's knife and ecraseur and deprived of the testes,--the
male sexual glands. From the day of this operation these two animals
(in every respect alike, except that one is unmutilated