The blood which escapes is certainly con verted to no positive use. No office can be assigned to it, such, for example, as has been suggested for the analogous escape of blood into the ripe ovisac — an effusion that has been termed the menstruation of the follicle.* But although the blood, after it has passed the uterine epithelium, is altogether lost, it may, by escaping, fulfil the negative purpose of affbrding relief to the congested capillaries of the uterus. For we find, from various kinds of evidence, that, at each menstrual period, all the uterine tissues become charged with a more than ordinary quantity of blood, and, therefore, with the materials necessary to those rapid growths which have been shown to commence as soon as impregnation has taken place. From the moment that the latter occurs, the mucous and other tissues of the uterus begin rapidly to expand, and the current of blood is diverted to new chan nels. There is then no overplus, until the whole cycle of generative acts, including lacta tion, is complete. The only observable break happens at parturition ; but after the balance of' the uterine circulation has been restored by the escape of blood at the time of labour, and by the lochia, there is again usually no redundance until the office of the mammary glands has ceased. Then, the activity of the ovaries recommencing, the periodical hyper walla of the uterine vessels returns, and the overplus is emitted in the form of menstrual blood, And thus, by each act of menstrua tion, the uterus is placed in a state of prepa ration for that profuse development of its tissues which impregnation may at any time of the succeeding interval call forth.
The office of the uterua in After menstruation, which is to be regarded as a process preparatory to impregnation, the next office of the uterus is that of receiving the seminal fluid, and apparently of conducting it to the Fallopian tubes, by which again it may, in rare instances, be carried as far as the ovary. To this office the form of the uterus appears to be well adapted in all its parts. For, first, the cervix uteri is so constructed as to lie in the centre of the upper dilated portion or fornix of the vagina, into w hich it projects to a distance of 3 —4"'. This dilated ex tremity, of the vag,ina forms a pouch sshich re ceives the extremity of the intromittent organ, and in this receptacle the seminal fluid is de posited. But, on account of the natural posi tion of the uterus, which lies in the axis of the pelvic brim, while the course of the vagina corresponds with that of the cavity and out let (fig. 433.), the cervix uteri is so directed (doN% nwards and backwards) as to cause the os uteri externum to be maintained in the very centre of this pouch, so that the seminal fluid will be retained in a situation in which it is most certain to flow through this orifice into the cervix.* But the cervical canal is traversed
by numerous furrows, which will act as so many channels, conducting the semen to the internal os, while the dilated central portion of that canal (fig. 424.) serves the purpose of a second reservoir.
It may also be readily believed that the ejaculatory act on the part of the male will suffice to carry the seminal fluid thus far, although the impetus with which it is propelled having been checked by the constriction caused by the external os uteri, would hardly suffice to carry it much beyond the more narrow bar rier existing at the internal os. Or if it should pass this second obstacle, the almost complete apposition of the walls of the uterus would prevent any considerable penetration of the semen further into the uterine cavity, so far as this is dependent on the act of ejaculation.
But this very apposition of the uterine walls may, in another manner, assist the onward progress of the semen, by inducing a kind of capillary attraction, such, for example, as will cause water to rise, to a certain distance, be tween two plates of glass placed in close con tact. The rigid walls of the human uterus, which are normally in such close apposition that sections made in certain directions scarcely suffice to display any appreciable cavity (figs. 426. and 427.), seem admirably adapted to fa vour this gradual rise of the seminal fluid be tween them towards the Fallopian tubes ; and thus a compensation is provided for that peri staltic movement, which, in some mammalia with a more intestiniform and less rigid uterus, appears, under the influence of the coitus, to affect alike the vagina, uterus, and Fallopian tubes*,and to suffice for the conveyance of' the seminal fluid from one extremity to the other of the generative track.
The action of the cilia of the uterine epi thelium cannot, in any way, contribute to this result, if those observations are correct which agree in assigning to them a movement such as would create a current from within out wards ; for it is obvious that such a motion would tend to retard rather than to advance the progress of the seminal fluid towards the Fallopian tubes.
If therefore any other power is needed to account for this movement, it must be sought in the action of the spermatic particles them selves. For, little adapted as their motions appear to anything like onward progression, yet they have been observed to contimie long after ejaculation, in the fluid found within the uterus and tubes, and even upon the ovary.f It has been also proved beyond doubt that by this power the spermatozoa penetrate the ovum itselft, and therefore to it may be attributed a certain share in the progress of the seminal particles through the uterus towards the ovi ducts, although this may not be a very con siderable one.