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 our advancing knowledge.

In these as in other respects the ovaries are precisely analogous to the testes.  They not only form the ova, but they elaborate for internal use a secretion which develops and maintains the special physical and mental qualities of womanhood, as the testicular secretion those of manhood.  Moreover, as Cecca and Zappi found, removal of the ovaries has exactly the same effect on the abnormal development of the other ductless glands as has removal of the testes.  It is of interest to point out that the internal secretion of the ovaries and its important functions seem to have been suggested before any other secretion than the sperm was attributed to the testes.  Early in the nineteenth century Cabanis argued ("De l’Influence des Sexes sur le Caractere des Idees et des Affections Morales,” Rapport du Physique et du Moral de l’Homme, 1824, vol. ii, p. 18) that the ovaries are secreting glands, forming a “particular humor” which is reabsorbed into the blood and imparts excitations which are felt by the whole system and all its organs.

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