'911.] THE MAMMALIAN OVARY. 231 



seems that pregnancy even favors the maturation of follicles. The 

 corpus luteum prevents, however, the rupture of the mature follicles. 

 Pregnancy as such does not prevent the rupture provided the corpus 

 luteum has been previously removed through excision. 



The structural changes in the ovaries are rhythmical and so reg- 

 ular that a careful histological examination of these organs enables 

 us to decide within a certain limit of accuracy at what period of the 

 sexual cycle the animal had been at the time of the removal of the 

 ovaries. 



Having established the normal cycle I turned more recently my 

 attention to its pathological deviations. It occurs in a certain num- 

 ber of animals — and I have observed this to happen among females 

 which showed no desire for copulation or in which notwithstanding 

 an accomplished copulation an ovulation did not follow — that the 

 follicles do not grow to maturity, but that they imdergo involution 

 before they reach their full size, and that all, or almost all the folli- 

 cles, become sclerosed, atretic, at a very early stage of their develop- 

 ment. Under these conditions, an ovulation is impossible and the 

 animal, in the ovaries of which such a deviation from the normal 

 cyclic changes exists, are at least temporarily sterile ; whether such 

 a pathological condition may ever lead to a permanent sterility, 

 future investigations must show. It will be readily understood that 

 here we have to deal with questions of the greatest importance to 

 the physiology of the sexual functions. 



In order to appreciate thoroughly the conditions under which 

 such abnormalities in the sexual cycle occur, it is necessary to pro- 

 duce the subnormal development of the follicles experimentally. Now 

 it is of interest to know that such a premature involution of the 

 ovarian follicles can be produced experimentally by burning a certain 

 relatively small part of the ovaries with the thermocautery. The 

 remaining larger part of the ovary remains apparently perfectlv well, 

 the cells functionate but the energy of growth of certain cells is 

 diminished and subinvolution of the follicles with resulting temporary 

 sterility follows. A comparable condition can be produced in tumors 

 through heating, or through the influence of certain chemicals exerted 

 in vitro as I found a number of vears ago. Under such conditions 



