B. After Impregnation. —Very different is the progress of the Graafian follicle after im pregnation has taken place. Here, although the changes which occur have no other intel ligible purpose than that of the final oblitera tion of the follicles, yet the process takes place much more slowly than it does when the ovipont has not been followed by conception. In this latter case, the metamorphosis of the follicle into the small yellow stellate organ takes place usually within a month from the time of rupture, and its subsequent reduction to the little white cicatrix previous to its total disappearance is completed in about the like period. But the follicle, which has discharged an ovum that has been afterwards inipregnated, is not obliterated in a shorter time usually than 13-14 months. During that tirne it appears to undergo a great and remarkable development. But a close examination shows that this is not true development, in the or dinary sense of the word. It is not a forward movement, progressing towards any new pur pose or end, but is only the sarne process of obliteration, conducted upon a larger scale, and with a greater abundance of materials than in the case of the ordinary follicles when im pregnation has not occurred.
Apparently the chief difficulty which has stood in the way of a clear comprehension of this has arisen from a want of sufficient consi deration of those altered circumstances in which the generative organs are placed after conception ; for, from the moment that im pregnation has occurred, all parts of the gene rative apparatus are brought under the influ ence of a common stimulus, and all manifest in a greater or lesser degree some progressive channe. This is more particularly observable in the internal organs, and especially in the uterus, which very soon receives a larger supply of blood. But the blood-vessels supplying the uterus inosculate so freely with those of the ovary, that the two organs may be practi cally regarded as deriving their blood from one common source. Each may be injected from the vessels of the other, and though only one set be selected, both are alike filled.
Hence it may be assumed that, although there is no direct continuity of texture be tween the ovary and the uterus, yet, under the influence of a common supply of formative material, as well as a common innervation, there may be established such a consent of action as will account, in some degree at least, for the differences which we are now about to consider; for when, after the discharge of the ovum from the ovary, impregnation fails, or has not been attempted, the internal organs, previously highly vascular, subside into a passive or quiescent state until the pe riod of the next ovipont approaches, when the uterus again exhibits the same condition of turgescence. But if impregnation has
taken place, then the turgescence of the ute rus, far from subsiding, only increases, and certain of its textures now become rapidly evolved. The reproductive act, however, does not commence in the uterus. The ovary is the seat of the first changes, and the uterus is only placed in a condition of readiness, on each occasion of the ovipont, to carry on and complete the process which has been com menced in the former organ. The absence of impregnation, on the one hand, is the cause of the failure of the further stages of the pro cess ; the occurrence of impregnation, on the other hand, establishes these stages ; conse quently the ovisac which is about to discharge, or one which has just discharged an ovum, and the uterus which is about to receive or which has just received that ovum, are both placed under similar conditions. Whatever influences the one in the direction of develop ment, affects the other also, to a certain de gree, in the same direction. Whatever, on the other hand, determines the retrogression of the one, determines, in like manner, the receding of the other. If the ovum has be come impregnated, the follicle which was the first birthplace of that particular ovum, and the uterus which subsequently receives and protects it, continue alike to suffer change. But if the ovum perishes, the recipient organ feels no stimulus, is not excited to further preparation, subsides into its former state of quiescence, and its producing capsule likewise shrinks, and finally disappears. If the inquiry be prosecuted further in the hope of eliciting some more satisfactory explanation of this re markable series of changes, the investigation will, in the present state of our knowledge, be found altogether to fail. The question, Cui bono continues unanswered, but the fact re mains, and the law appears to be invariable.
When conception has followed the discharge of an ovum frorn the ovarium, the follicle which produced it closes in the same manner as when conception has not occurred, but it does not shrink rapidly, as in the latter case. On the contrary, the inner coat or original ovi sac continues to increase in thickness, in conse quence of a still larger deposit of yellow oil granules in its substance. The outer coat of the follicle or tunic of the ovisac suffers no change ; but upon the interior of the ovisac, and therefore lining the cavity, is formed a membrane, the origin and nature of which will be presently considered ; or else it may happen that the cavity becomes obliterated by the organisation of the clot by which it had been at first filled.