232
WILLIAM C. YOUNG
effective (391). Testes of 26- to 31-day female guinea pigs secrete
androgen at this time (392). In the rat the period of maximum susceptibility is about the same, but because of the short gestation period it
appears from presently recorded data to be postnatal rather than prenatal (392a,b). Detailed reports of the behavior of female rats to which
testosterone was administered during the period of maximum susceptibility have not appeared, but in general the alterations were similar to
those described for the guinea pig. Enhancement of the capacity to
display masculine behavior and suppression of the capacity to display
feminine behavior were seen
(392a,c,d,e).
The fetal testicular substance having these effects on the developing
genital tracts and neural tissues has not been identified. Had discovery
of the suppressing action of testosterone propionate on the tissues mediating mating behavior in the female come first, the assumption would
have followed that the hormone of the fetal testis is essentially similar
to that of the adult testis. On the other hand, testosterone propionate,
while stimulating development of the male genital tract and the organization of the neural tissues mediating sexual behavior in the male,
does not have the suppressing action on the Miillerian ducts which Jost
(393-395) believes is possessed by the fetal testis. However, see Wells'
(384) discussion of the point. In an effort to account for this inconsistency the suggestion has been made that the hormone produced by
fetal testes is different from that produced by adult testes (384, 393,
396).
During attempts to feminize male guinea pigs, it was found that
exogenous estrogens terminate pregnancy (388). For this reason more
information has come from investigations in which the rat was used.
The substance of several reports indicates that male rats injected with
estradiol benzoate at 5 days of age exhibited markedly diminished or
even an absence of masculine behavior (392c,d,e, 396a). When placed
with vigorous intact males, the males treated in infancy with estradiol
displayed an appreciable degree of feminine behavior in the form of
lordosis (396a). These data suggested feminization of the male by the
estrogen, but recalling the embryological evidence that sexual differentiation is the result of stimulation by testicular rather than by ovarian
hormones, Whalen (396a) suggested that the female-like behavior might
have been a consequence of functional castration. Unknown to him, an
experiment designed to test this possibility had just been completed by
Grady and Phoenix (33a, 396b). Their results revealed that in the
absence of testes during the first 5 days of infancy, the male rat develops
a capacity to display strong feminine responses. The possibility that
estrogen has a feminizing action that can be superimposed on the
WILLIAM C. YOUNG
effective (391). Testes of 26- to 31-day female guinea pigs secrete
androgen at this time (392). In the rat the period of maximum susceptibility is about the same, but because of the short gestation period it
appears from presently recorded data to be postnatal rather than prenatal (392a,b). Detailed reports of the behavior of female rats to which
testosterone was administered during the period of maximum susceptibility have not appeared, but in general the alterations were similar to
those described for the guinea pig. Enhancement of the capacity to
display masculine behavior and suppression of the capacity to display
feminine behavior were seen
(392a,c,d,e).
The fetal testicular substance having these effects on the developing
genital tracts and neural tissues has not been identified. Had discovery
of the suppressing action of testosterone propionate on the tissues mediating mating behavior in the female come first, the assumption would
have followed that the hormone of the fetal testis is essentially similar
to that of the adult testis. On the other hand, testosterone propionate,
while stimulating development of the male genital tract and the organization of the neural tissues mediating sexual behavior in the male,
does not have the suppressing action on the Miillerian ducts which Jost
(393-395) believes is possessed by the fetal testis. However, see Wells'
(384) discussion of the point. In an effort to account for this inconsistency the suggestion has been made that the hormone produced by
fetal testes is different from that produced by adult testes (384, 393,
396).
During attempts to feminize male guinea pigs, it was found that
exogenous estrogens terminate pregnancy (388). For this reason more
information has come from investigations in which the rat was used.
The substance of several reports indicates that male rats injected with
estradiol benzoate at 5 days of age exhibited markedly diminished or
even an absence of masculine behavior (392c,d,e, 396a). When placed
with vigorous intact males, the males treated in infancy with estradiol
displayed an appreciable degree of feminine behavior in the form of
lordosis (396a). These data suggested feminization of the male by the
estrogen, but recalling the embryological evidence that sexual differentiation is the result of stimulation by testicular rather than by ovarian
hormones, Whalen (396a) suggested that the female-like behavior might
have been a consequence of functional castration. Unknown to him, an
experiment designed to test this possibility had just been completed by
Grady and Phoenix (33a, 396b). Their results revealed that in the
absence of testes during the first 5 days of infancy, the male rat develops
a capacity to display strong feminine responses. The possibility that
estrogen has a feminizing action that can be superimposed on the