2. TheParenchsyma or Stronza,( fig. 371.c,and fig. 372. s) constitutes the proper tissue of the ovary. It lies immediately beneath the tunica albuginea, and fills up the whole of the inter mediate space between the ovisacs, to which it acts as a germ bed, protecting the ova from injury, and serving for the conveyance of blood vessels to the ovisaes. This tissue is some times of a pale-pink, but more often of a bright-red colour, from the large number of blood-vessels which it contains, whose ar rangement proceeding from within, and radi ating outwardly in all directions, gives to this titsue, when viewed by the naked eye or by a common lens, the appearance of being formed into bundles or laminm.
The microscope, however, serves to resolve this tissue into its true elements. When so examined, the stroma is found to be composed mainly of blood-vessels, to which a great part of its strength and toughness is due, the in termediate spaces being filled up by a fibrous structure not separable into bundles, like ordinary connective tissue, and having no dis tinct fibrillar arrangement, its chief elements being single white fibres of ordinary connective tissue, numerous fusiform embryonic fibres,and elliptical and round cells or granules, the whole being coherent and strongly united together.
3. The Graafian Vesicles. Folliculi ovarii, s. Graafiani, s. Ovisacci.—When the substance of a healthy ovary is divided by a clean incision, if the subject be not too advanced in life, the section will be found to have included several vesicles varying in diameter from 4"' down to sacculi of microscopic minuteness. These to a very recent date it appears to have been assumed that their number was limited. They were usually estimated at 12 to 20in each ovary; and it was generally supposed that, when these were exhausted by child-bearing and miscar riage, the power of procreation of necessity ceased. More recent and careful observation, however, has shown that the number of vesi cles in each ovary amounts in healthy organs to 30, 50, 100, or even 200; whilst in very young subjects their numbers exceed all power of accurate computation.
The vesicles are most easily displayed in the adult ovary by making a perpendicular section through the organ in the direction of its longer axis. In this way the largest num ber will have been divided by one incision ; and such a section, as in fi'g. 372., will often suf fice to exhibit 8 to 12 vesicles of different sizes. On submitting the section, however,
to the microscope, others of a smaller size, which had previously escaped attention, will be brought into view ; and in continuing the incisions in various directions, fresh vesicles will be laid open of various sizes and in dif ferent stages of development. If the ovary of an infant be selected for observation, the organ should previously have been hardened by maceration for several days in spirit. A clean section is thus easily obtained by a sharp knife; and if this be examined by a 1-inch ob ject glass, the little spherical ova, coagulated by the action of the spirit, will be readily seen, each one lying in its proper ovisac, by which it is immediately surrounded, and the whole so closely set and so numerous that a single sec tion suffices to display several hundred of them at one view (fig. 373.).
vesicles, familiarly known as the ova of De Graaf, although the credit of antecedent ob servation is certainly due both to Vesalius * and Fallopius -1., are variously distributed through the ovary according to the age of the individual. In infants and young subjects, the ovisacs are found only at the periphery of the organ, where they form a thick rind, the inte rior of the ovary being occupied only by blood vessels and stroma. But after puberty the division into a cortical and central part be comes less distinct, the ovisacs becoming buried deeper in the stroma, so that occasionally, in making sections of the part, they are encoun tered as deep as the base of the organ. They are always, however, most numerous near the surface.
The number of developed vesicles contained in each ovary, and visible to the naked eye, varies considerably' in different subjects. Up The Graafian follicle, when not subjected to pressure from surrounding parts, or from ad jacent vesicles, is spherical or oval in form, (fig. 371. DD, andfig. 372. g) and consists of cer tain tunics and contents. The number and composition of its coats have been variously described by recent observers ; and upon this subject a difference of views would be of com paratively little importance, if upon a right solution of this question did not depend the clear comprehension of those changes which occur in the Graafian follicle during preg nancy, and which result in the formation of the body termed the corpus luteum.