362 MENSTRUATION, [BOOK iv. 



masses, forming the latter part of the menstrual flow, which with 

 tlu- diminution of the haemorrhage becomes less and less coloured. 

 Tlit' amount of mucous membrane which is thus shed appears to 

 vary oxtivmi'ly in different cases; according to some authors the 

 loss may be so complete, that the bases only of the uterine glands 

 are left, and from the epithelial cells lining these the regeneration 

 of the new membrane is said to take place. The escaped ovum, 

 if no spermatozoa come in contact with it, dies, the uterine 

 membrane returns to its normal condition, and no trace of the 

 discharge of an ovum is left, except the corpus luteum in the ovary. 



937. It is difficult to resist the conclusion that there is 

 a causal connection between the changes in the ovary leading to 

 the escape of an ovum, and the changes in the mucous mem- 

 brane of the uterus leading to the menstrual flow; looking at 

 the matter from a teleological point of view, we may say that 

 the changes in the uterus appear to be preparatory for the recep- 

 tion of the ovum. But the exact connection between the two sets 

 of changes is far from clear. For it is by no means certain that 

 menstruation, in the human subject at all events, is always ac- 

 companied by a discharge of an ovum; indeed it is stated that 

 menstruation has, in certain cases, continued after what appeared 

 to be complete removal of both ovaries. On the other hand the 

 fact that impregnation may follow upon a coitus effected in the 

 interval between two menstrual periods, at which time presumably 

 no ovum is present in the uterus for the spermatozoa to act upon, 

 has been used as an argument that the act of coitus itself may 

 lead to the escape of an ovum independent of menstrual changes. 

 Since however the time during which both the ovum and the 

 spermatozoon may remain in the female passages alive and function- 

 ally capable is considerable, probably extending to some days, coitus 

 effected either some time after or some time before the menstrual 

 escape of an ovum might lead to impregnation and subsequent 

 development of an embryo ; hence no great stress can be laid upon 

 this argument. And a somewhat similar argument drawn from 

 the experience that pregnancy may occur while menstruation is 

 suspended by lactation or otherwise may be met by the reflection 

 that the uterine mucous membrane is by the circumstances 

 unfitted to respond to the uterine changes. 



In any case it would seem that it is not so much the mere 

 escape of the ovum, as the changes in the ovary of which the 

 escape of the ovum is the culminating point, which we must 

 regard as the cause of the uterine changes. If we allow ourselves 

 to admit such a causal connection, we may conclude that in these 

 phenomena of menstruation we have to deal with complicated 

 reflex actions affecting not only the vascular supply, but appa- 

 rently in a direct manner, the nutritive changes of the organs 

 concerned. Our studies on the nervous action of secretion render 

 it easy for us to conceive in a general way how the several events 



