The augmentation in bulk of the follicle is, in the first instance, due almost entirely to an increase in its fluid contents. It is probable that this fluid is supplied by the minute ca pillaries with which the ovisac is furnished, and which, long before the vesicle has attained its full diameter, appear in the form of a rich network upon its inner surface, giving to the latter a bright red colour.
And now a thickening of the walls of the follicle becomes very manifest, accompanied by an exudation of blood which collects in the interior of the sac. The period at which this escape of blood commences is variable. Some times it may be seen in follicles of not more than le' diameter, but more frequently when they have attained a size of about 3/".
As this exudation of blood takes place at a period certainly antecedent to the rupture of the follicle, it cannot be traced to vessels lacerated during that process, but must pro ceed from the congested capillaries just de scribed. It resembles arterial blood, and is rich in globules, which at first remain free and distinct ; but when the distension of the fol licle has become considerable, the blood co agulates into a dark-red clot.
This pouring-out of blood has been termed the rnenstruation of the follicle ; but beyond the purpose of increasing the distension of the latter, preparatory to its rupture, no use has been assigned to it, except by Pouchet, who maintains that in the sow the ovum lies at the bottom of the follicle, instead of near its upper or free surface ; and that as the sanguineous exudation increases, it collects _between the inner surface of the ovisaC and the membrana granulosa, and so carries up wards the latter, together with the ovum which is lodged upon it. He asserts, further, that in proportion as this exudation increases, the albuminous fluid previously occupying the follicle is absorbed, until the entire cavity be comes filled with blood.
The result of this process is, that the ovum, previously lying at the bottom, is now trans ported to the upper part of the follicle, imme diately beneath the point at which the rupture of the walls is about to take place.
Notwithstanding the minuteness of Pou chet's description, its accuracy, so far at least as concerns the supposed purpose of this exu dation of blood, has been called in question. The fact, however, cannot be disputed, that, in many animals, as well as in man, the follicle does contain blood, often in considerable quantity., previous to its rupture. And this is
a very important point, because it serves to refute the statement of some who maintain that the presence of blood, or of a clot, within the follicle, affords certain evidence that the rupture of the latter, together probably vuith the escape of the ovum, has already occurred. Barry also, in his researches upon the rabbit, says, that after certain of the ovisacs have discharged their ova, " some of the larger Graafian vesicles, remaining unbroken, are fre quently found to contain a considerable quan tity of blood. Such spots, he observes, have been noticed by several observers, who sup posed them to indicate the Graafian vesicles from which ova were destined to be expelled.
Thus Barry's prior testimony serves to confirm that of Pouchet and others, to the effect that the blood found within the follicle does not result from its rupture, but that it is there antecedent to that process.
Sonte other changes which occur ,in the follicle previous to its rupture may here be noticed. The thickening just spoken of takes place in the inner membrane, or that which constituted originally the ovisac. This thick ening is sometimes so considerable as to in crease the diameter of the follicular walls to three times their original amount. At the same time, their contour becomes somewhat undulating, and their colour approximates to that of the buffy coat of the blood.
While these changes are going on in the substances and in the contents of the follicle, preparation is being made externally for the rupture at a certain part of the parietes. The base of the follicle continues to be imbedded in the substance of the ovary (fig. 379.), but the upper portion projects free above this, being covered only by the usual ovarian in vestnients. Here, at the more salient portion of the projecting vesicle (fig. 379.), an in creased vascularity is observable. The peri toneum and sublying tissues become exceed ingly red, and an abundance of blood is observed in the numerous capillaries which are now visible upon the summit of the vesicle. After this, the fibres of the ovarian coverings become gradually separated, preparatory to their com plete laceration. The tunics also of the fol licle itself become perceptibly thinner at this spot, which corresponds with the situation of the ovuin — always, at this period, lying im mediatelY beneath it.