s _Elements of Physiology_ that the sperm
accumulated in the seminical vesicles is pumped back into the blood, and
thus produces the beard and the hair together with the other surprising
changes of puberty which are absent in the eunuch. The reabsorption of
semen can scarcely be said to be a part of the modern physiological
doctrine, but it is at least now generally held that the testes secrete
substances which pass into the circulation and are of immense importance
in the development of the organism.

The experiments of Shattock and Seligmann indicate that the semen and its
reabsorption in the seminal vesicles, or the nervous reactions produced by
its presence, can have no part in the formation of secondary sexual
characters. These investigators occluded the vas deferens in sheep by
ligature, at an early age, rendering them later sterile though not
impotent. The secondary sexual characters appeared as in ordinary sheep.
Spermatogenesis, these inquirers conclude, may be the initial factor, but
the results must be attributed to the elaboration by the testicles of an
internal secretion and its absorption into the general circulation.[142]

When animals are castrated there is enlargement of the ductless glands in
the body, notably the thyroid and the suprarenal capsules.[143] It is
evident, therefore, that the secretions of these ductless glands are in
some degree compensatory to those of the testes. But this compensatory
action is inadequate to produce any sexual development in the absence of
the testes.

We see, therefore, how extremely important is the function of the testis.
Its significance is not alone for the race, it is not simply concerned
with the formation of the spermatozoa which share equally with the ova the
honor of making the mankind of the future. It also has a separate and
distinct function which has reference to the individual. It elaborates
those internal secretions which stimulate and maintain the physical and
mental characters, constituting all that is most masculine in the male
animal, all that makes the man in distinction from the eunuch. Among
various primitive peoples, including those of the European race whence we
ourselves spring, the most solemn form of oath was sworn by placing the
hand on the testes, dimly recognized as the most sacred part of the body.
A crude and passing phase of civilization has ignorantly cast ignominy
upon the sexual organs; the more primitive belief is now justified by