50 S. ZUCKERMAN 



the body, thymus and spleen during the three months which 

 follow sterilization, which correspond to those that occur after 

 surgical removal of the ovaries. Further experiments showed 

 that these indications of oestrogenic activity continue after 

 bilateral adrenalectomy, but cease after removal of the X-ray 

 sterilized ovaries — which presumably are therefore responsible 

 for the secretion of the hormone. 



In effect, what all this adds up to is that the capacity of 

 the ovary to secrete sex hormone is neither necessarily, nor 

 absolutely, dependent upon the presence of germinal elements. 

 Earlier histological studies of the ovaries of mice that had 

 been X-irradiated at birth or at the age of three weeks had 

 indicated that the cells which are responsible for the continued 

 secretion of oestrogen after the elimination of the follicular 

 system are those which are derived from what is described as 

 "the first post-irradiation proliferation" of the germinal 

 epithelium (Brambell, Parkes and Fielding, 1927a, b). The 

 tissue produced by this proliferation is "almost indistinguish- 

 able from true luteal tissue . . . the epithelial cells becoming 

 like luteal cells with connective tissue elements of the sheath 

 growing in amongst them like the thecal cells of the corpus 

 luteum." Such proliferations do not occur in the adult ovary. 

 The X-irradiated adult mouse which continues to undergo 

 oestrous cycles was held by Brambell and Parkes (1927) to 

 be under the influence of oestrogen produced by "inter- 

 follicular tissue " and "follicular derivatives ". The latter two 

 elements are, for all practical purposes, indistinguishable from 

 each other, and form the main part of the sterilized ovary. 

 Histologically they closely resemble the cells seen in mice 

 irradiated before puberty, and which are derived from the 

 cords of the first proliferation. 



We have found that even when no luteal-like cells are present 

 in rats sterilized before puberty, and when no cyclical changes 

 occur in the vaginal smear, the vaginal closure membrane 

 nevertheless breaks down (Mandl and Zuckerman, 1956c). 

 Since treatment with oestrogen makes it do so precociously 

 (Allen and Doisy, 1924), the obvious inference would be that 



