840 MENSTRUATION. 



only by a congestion or erection of the ovary and Fallopian tube, but also 

 by marked changes in the uterus, especially in the uterine mucous mem- 

 brane. While the whole organ becomes congested and enlarged, the mucous 

 membrane, and especially the uterine glands, are distinctly hypertrophied. 

 The swollen internal surface is thrown into folds which almost obliterate the 

 cavity ; and a hemorrhagic discharge, often considerable in extent, constitut- 

 ing the menstrual or catamenial flow, takes place from the greater part of 

 its surface. The blood as it passes through the vagina becomes somewhat 

 altered by the acid secretions of that passage, and when scanty coagulates 

 but slightly ; when the flow, however, is considerable, distinct clots may 

 make their appearance. The swollen and hypertrophied mucous membrane 

 then undergoes a rapid degeneration, and is shed, passing away sometimes in 

 distinct masses, forming the latter part of the menstrual flow. The loss of 

 the mucous membrane is 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. It is not certain that menstrua- 

 tion, in the human subject at all events, is always accompanied by a dis- 

 charge of an ovum ; indeed cases have been recorded in which menstruation 

 continued after what appeared to be complete removal of both ovaries. And 

 it seems probable also that under certain circumstances, e. g., coitus, a dis- 

 charge of an ovum may take place at other times than at the menstrual 

 period. Since, however, the time during which both the ovum and the 

 spermatozoon may remain in the female passages alive and functionally 

 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 the fact that impregnation may follow upon coitus at some time after 

 or before menstruation is no very cogent argument in favor of the view that 

 such a coitus has caused an independent escape of an ovum. The escape of 

 the ovum is said to precede, rather than coincide with or follow, the cata- 

 menial flow. If no spermatozoa come in contact with the ovum it dies, the 

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

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



780. It is obvious that in these phenomena of menstruation we have 

 to deal with complicated reflex actions affecting not only the vascular 

 supply, but, apparently in a direct manner, the nutritive changes of the 

 6rgans concerned. Our studies on the nervous action of secretion render it 

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

 about. It is no more difficult to suppose that the stimulus of the enlarge- 

 ment of a Graafian follicle causes nutritive as well as vascular changes in 

 the uterine mucous membrane, than it is to suppose that the stimulus of food 

 in the alimentary canal causes those nutritive changes in the salivary glands 

 or pancreas which constitute secretion. In the latter case we can to some 

 extent trace out the chain of events ; in the former case we hardly know 

 more than that the maintenance of the lumbar cord is sufficient, as far as 

 the central nervous system is concerned, for the carrying on of the work. 

 In the case of a dog in which the spinal cord had been completely divided 

 in the dorsal region while the animal was as yet a mere puppy, " heat " or 

 menstruation took place as usual. 



