252 CHARLES R. STOCKARD AND G. N. PAPANICOLAOU 



These occuiTences argue very decidedly against the theory 

 ad\'anoed by Fraenkel ('03), and until recently supported by a 

 number of other investigators. Fraenkel believed that the 

 corpus luteum is the cause of the menstrual condition, producing 

 through its secretion the destructive changes in the uterus and 

 vagina. Such a supposition does not in any sense accord with 

 the phenomena as they appear in the gTiinea-pig. If there is to 

 be ascribed to the secretion of the corpus luteum an action upon 

 the uterine and vaginal mucosae such an action is not of an in- 

 jurious but of a protective nature. As we shall bring out further, 

 the most plausible opinion of the action of- the corpus luteum in 

 the ovary itself, may also be interpreted as of a protective nature 

 since it seems to prevent rupture of the Graafian follicles and the 

 discharge of the ova. The facts obtained in the present inves- 

 tigation might not fully warrant the position that the corpus 

 luteum really exerted an actively protective influence over the 

 uterine mucosa, but they certainly in no sense suggest, and actu- 

 ally speak against, any injurious action on the mucosa by the 

 secretion of the corpus luteum. 



At the same time it is difficult to maintain that the absence of 

 the protective action of the corpus luteum is the only or actual 

 cause of the oestrous activity. The cause of oestrous is very 

 probably more complex and the definitely regular rhythmical 

 changes which take place in the uterus and vagina of the guinea- 

 pig can not be fully explained as due alone to the degenera- 

 tion of the corpus luteum. The absence of the luteal secretion 

 possibly merely permits the uterine flow to occur as it seems also 

 to permit the rupture of the ripe Graafian follicles. While the 

 real mechanism determining the uterine reaction is a more 

 complex factor and relatively independent, but affected in its 

 expression by a close inter-relationship with the ovaries. 



The various theories, however, which attempt to localize the 

 cause of the uterine changes in the ovary are not in any case fulh' 

 in accord with all the facts. It is of course true that the existence 

 of the ovaries is necessary for the normal development and 

 function of the uterus and vagina, and also that the removal of 

 both ovaries leads to a disappearance of the typical oestrous 



