INCREASED RESISTANCE TO SYPHILIS IN THE RABBIT FOLLOWING PROLONGED ADMINISTRATION OF URINARY ESTROGENS I. FEMINIZING EFFECTS OF ESTROGENS ON ADULT MALE RABBITS

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Abstract
The course of syphilitic infection in 2 groups of adult [male] rab-bits, homogeneous as to breed, age, and nutrition, was studied. Before intratesticular inoculation with Treponema pallidum, one group was subjected to prolonged treatment with an estrogenic substance prepared by extracting human P. U. with butyl alcohol. The animals were injected daily with the ether soluble fraction of this extract dissolved in olive oil. The estrogenic content was assayed by the use of the vaginal growth effect on ovariectomized albino rats. Physiological effects of the estrogenic substance were manifest in growth of the nipples and mammary glands together with stimulation of lactation, feminization of external genitalia and atrophy of the testes, development of dewlap, a 2[degree] sexual characteristic of the [female] rabbit, and in certain changes of psychosexual behavior. Among the estrinized rabbits, early manifestations of syphilis were much milder and followed a shorter course than among sexually intact rabbits. Estrinized animals showed an increasing ability to withstand the injurious effects of the disease the longer they were treated. This was shown by the greater frequency with which they failed to develop generalized foci of infection. Resistance to disease developed by the testis was the most noteworthy modification of the reaction to infection, although skeletal and cutaneous tissues behaved in a similar manner.