The other circumstance which it may be important here to notice is, that the yellow structure is no new nor superadded part, but is the ovisac itself, altered by the gradual de posit in its texture of a yellow oil, which at length accumulates to such a degree as to con vert this previously translucent wall of the follicle into an opaque 3 ellow membrane or coat. But neither in any of these stages, nor in any subsequent ones, is there interposed either between the walls of the follicle or be tween these latter and the surrounding ova rian stroma, any new substance or body of any kind. The yellow colour is confined to the inner coat of the follicle, nor have I ever seen it in any one instance penetrating to the outer coat or covering of the ovisac. There is only one new coat formed, which will be hereafter described ; and that coat, often of considerable thickness, is a part entirely superadded, which, after a certain stage in the metamorphosis of the follicle, is applied in the inner side again of the yellow coat, to which it forms a lining. This, although a new forma tion, is also, as will be presently shown, con structed out of materials existing in the fol licle before its rupture.
The final purpose of the Graafian follicle being now accomplished, it may seem a matter of comparatively little interest or importance, in a physiological point of view, to trace its ultimate conditions ; for the changes which this structure next undergoes have for their object solely its obliteration. But the process of obliteration or retrogression does not, like the process of development, take place under all circumstances alike. Here the influence of impregnation is exhibited in a degree so remarkable as to have given rise to a general belief that the changes experienced by the follicle, when impregnation has accompanied or followed its rupture, are essentially different in their nature and character from those which ensue when impregnation has not taken place ; whereas these differences, it will be shown, are differences chiefly of degree; and yet they are so considerable as to have called forth almost as great a share of attention as has been given, perhaps, to any structure in the hurnan body.
But great as is the interest attached to this structure on account of the evidence which it may afford of the previous occurrence or non occurrence of impregnation, yet, so various are the views and statements of those who have specially directed their attention to the subject, that neither among physiologists, pa thologists, nor medical jurists, can it be said that there is at present any concord of opinion or common ground of understanding.
Admitting, however, for the present that there is a marked difference observable in the changes which the Graafian follicle undergoes, according as impregnation has or has not ac companied or followed the escape of the ovum, we thereby obtain a starting-point, or rather a point of divergence, from which we may follow out these changes in two dif ferent series : the one series will include the alterations in the follicle which ensue when impregnation fails. or does not oc cur ; the other, those which it experiences in consequence of impregnation having taken place.
Fourth Stage. Period of Decline and Obli teration of the Graafian Follicles..
A. Without Impregnation.—This constitutes the first degree of the- descending scale in the history of development of the follicle. Im mediately after the escape of the ovum, the inherent contractility of the tunica albugi nea of the ovary occasions a diminution in the prominence of the lacerated vesicle. The margins of the opening become approxi mated in consequence of the collapsing of the walls, and from the edges of the laceration there occurs a slight fibrinous exudation which causes them to become agglutinated. If the aper ture has been of considerable size, and no clot remains in the cavity to keep its walls from collapsing, the process of obliteration may proceed rapidly ; but if a clot remains, and especially if it is of considerable size, it will serve to support the walls, and prevent them from quickly shrinking.
These different conditions will for a time affect the new disposition which the inner membrane of the follicle takes soon alter the rupture is complete. In proportion as the cavity is empty, the elasticity of the outer fibrous coat will, by its retraction, occasion a diminution of the cavity; but the inner coat, having already increased during the growth of the follicle in a greater degree than its outer covering, will now, in this collapsed and nearly empty condition of the sac, suffer the same change that would result from en closine a large bladder within a smaller one.
The inner coat becomes folded, and forms convolutions, which increase and become deeper in proportion as the retractility of the external tunic increases.
These convolutions in the inner and now yellow coat of the follicle are so distinct and striking (fig. 385.) as to have suggested those comparisons with the cerebral convolutions which so many authors have employed in describing this change ; for the colour, as well as the nature and arrangement of the foldinrzs, constituting ridges and sulci, produce an exact rniniature resemblance to the surface of the brain.