After conception it is probable that the ac tual diameter of the follicle does not at any time materially increase. So great, however, are the variations in its size in different sub jects, that this point scarcely admits of being accurately determined. The Graafian follicle may, at the time of rupture, occupy I., -a, or t of the entire ovary. These at least are the dimensions which it is usually found to have, in different instances, during the first four months of pregnancy ; but after this period the process of diminution begins to be percep tible. All the changes which are now observ able in regard to form, solidity, and other par ticulars obvious to the unaided senses, and all the histological changes are to be looked for within the outer coat of the follicle. The latter appears to suffer no alteration, but simply to follow the movements of its contained parts, around which it remains loosely applied. The ovisac, however, or inner coat, rapidly in creases in thickness, in consequence of a more considerable accumulation in its texture of the same yellow oil vvhose deposition had be gun in it long before the follicle had ruptured, and when it was only approaching the surface of the ovary.
This thickening of the inner follicular coat is followed by a twofold result. The mem brane, being confined by its outer tunic, now no longer distensible, as well as by the surround ing stroma into which the vesicle has now begun to sink, becomes more deeply plicated ; and since it can no longer extend outwardly-, it must of necessity encroach upon the cavity within. The latter thus becomes sensibly diminished, whilst the entire thickness of its boundary wall is in like proportion increased.
At the end of the first two months of ges tation, the folliele possesses considerable soli dity. The wavy and plicated condition of the yellow ovisac is now less distinct. The whole of this coat exhibits the appearance of a thick yellow layer, still occasionally traversed by numerous little blood-vessels, which run across it in straight lines from without inwards as far as its inner surface. The larger of these vessels probably do not actually pierce the yellow coat, but lie between the sulci, repre senting the original folds of the ovisac, and which, now pressed back to back without being yet obliterated, would still serve for the conveyance of blood-vessels to different parts of the tunic.
These changes continued to be in a certain sense progressive until the tburth month of gestation, about which time the Graafian fol licle is usually considered to attain its highest state of development. But if the term de velopment be admitted, it should be remem bered that the only apparent purpose of these and other chanaes which ensue is still the ob literation of the structures in which they occur. The process of obliteration, however, has at this time not proceeded so far as to have caused the removal or even diminution of any of the original parts composing the follicle, whilst soine new structures are super added or produced by metamorphosis of the original materials.
The follicle at this period generally affords the best opportunity for observing the changes which result from impregnation. It may therefore be selected for a critical examination of the subject.
The external condition of the ovary in which such a follicle is contained serves at once to point out the precise seat which the structure occupies. Not only is the entire ovary larger than that of the opposite side, but it appears more swollen, and is perceptibly harder in one particular spot; over or near this spot a cicatrix may still be visible, and in its immediate neighbourhood are often found some serpentine vessels. If, now, a section be made of the ovary in this situation so as not to pass through the centre, but to include only a portion of the circumference of the follicle, the latter will present the condi tion represented infig. 386. The follicle, in the
form of a little globe, is seen to occupy about a fourth part of the ovary. Its solidity and spherical form cause it to project considerably above the surface of the section. In this way is exposed the outer coat by which the follicle is bounded. Upon this coat numerous blood vessels, derived from the ovarian stroma, ra mify. It is the tunic of the ovisac, the origi nal outer coat of the Graafian follicle, which in all the transformations of the latter suffers no change, until the time arrives when thE whole body finally shrinks and disappears, The position and relations of this coat to surrounding parts leave no room for doubt as to its identity. Nothing bounds it externally but the stroma of the ovary. Nothing lines it internally but the yellow ovisac. Neither between its outer nor its inner surfaces, and the corresponding, structures just named, is there at any time found any substance or me dium interposed. This coat has undergone no material thickening, and its histological elements are simply those of the outer coat of the follicle, the same as before impregna tion has occurred.
Proceeding inwards, the next coat is yel low ; it has a nearly uniform thickness of le'. In its substance may still be seen traces of the original foldings or convolutions. These are more easily shown upon the sur face of the first section (fig. 386.), but are less obvious in one carried deeper so as to include the centre of the follicle, where the coalesce into larger drops that float to the surface of the fluid. The substance of the preparation also is everywhere pervaded by the oil drops which obscure its structure, and prevent further examination in this state. The preparation, having been treated next by ether, and subsequently washed in alcohol and replaced in water, it is found that the oil has entirely disappeared. The principal portion of the remaining substance has the appearance of a granular membrane, but in many places slightly wavy lines of connective tissue are perceptible. From the margins project in rnany places flattened bands composed of 8-10 filaments of common connective tissue, united by membrane, and having attached to them nunierous granules. Separate fibres also appear at the margin of the preparation, but only from forcible detachment. Treated fur ther by acetic acid, the oil globules, as well as the fibres, have totally disappeared. The course of the latter is now only indicated by numerous lines of round, oval, or elongated nuclei (fig. 388.), which are everywhere abun dantly seen attached to a fine, structureless, transparent membrane. The outlines of the coat shows greater solidity (fig. 387.). Up to this time, however, and sometimes later, the vessels still traversing this coat in the lines of its former convolutions may be traced in many specimens, and the capillaries may still be filled by a successful injection to such an extent as to render the whole mass crimson.* Exa mined by the microscope, the following results are obtained:—The yellow coat, 1-11"' thick, is soft, swells in water, and is easily torn into fragments which nevertheless hang together, being connected by a tough flexible medium. During this process numerous oil droplets escape, and form, with the drop of water in which the preparation is placed, a highly re fractive fluid. This fluid, when examined, is seen to contain numerous particles of inap preciable size endowed with molecular motion, minute granules, and oil globules, which are at first also very minute, but soon collect and nuclei are very sharp and distinct, and within them are contained one or two nucleoli. This coat is traversed by numerous blood-vessels and capillaries, and to their coats in all proba bility many of these nuclei belong.