52 S. ZUCKERMAN 



These observations seem to leave little doubt that the 

 mechanism of secretion is different in an X-irradiated as 

 compared with a normal ovary. Not only does it not re- 

 spond to gonadotrophic stimulation like a normal ovary, but 

 at no time (to judge, for example, by the size of the uterus) 

 does it secrete as much oestrogen as a normal ovary. Since 

 neither recurrent periods of vaginal cornification nor per- 

 sistent cornification continues indefinitely after X-irradi- 

 ation, it is also clear that the X-irradiated ovary becomes 

 progressively incapable of secreting at all. This conclusion 

 leaves open the general question whether the decline in 

 secretory capacity is due to the elimination of the germinal 

 elements of the ovary, or to damage inflicted on other ovarian 

 cells by the X-irradiation. At the moment it is difficult to 

 see how this particular problem can be answered. A decision 

 could possibly be based on experiments in which rats are 

 irradiated in a carefully graded series, so that their post- 

 irradiation behaviour could be related to the amount of 

 damage suffered by their ovaries. 



Conclusion 



From the fact that reproductive life in higher mammals is 

 of shorter duration than life itself; from the knowledge that 

 fertility in mammals, including man, reaches a peak in early 

 maturity and then gradually declines; from the observation 

 that the senescent ovary cannot be reactivated by any known 

 hormonal treatment ; and from the experimental data reported 

 in this paper, one can only conclude that in general the ovary 

 is a transient tissue with little regenerative capacity, not only 

 with respect to its germinal but also to its secretory functions. 

 The period over which the ovary is a regenerating structure, 

 in the sense that it is able to produce oocytes, may vary from 

 one mammalian species to the other, but, in general, it is an 

 organ which is more senescent, or potentially more senescent, 

 than the testis, both from the germinal and the secretory 

 points of view. 



