1 62 Veterinary Obstetrics 



layer of endothelium-like cells or of a concentrically arranged double layer. 

 From the primary follicular epithelium there develops from the cells a cy- 

 lindrical epithelium, which thus forms several layers. Regarding the origin 

 of the follicular cells, opinions vary. While, in the lower vertebrates, these 

 cells certainly originate from the germinal epithelium and this source for 

 the mammalia is accepted by manj' investigators, KoUiker, Rouget and 

 Biihler believe that, in the formation of the follicular epithelium, the me- 

 dullary fibres, or genital portions of the Wolffian bodies, plaj' an important 

 part, or, indeed, in the case of the dog, cat and fox, constitute the exclusive 

 source of these cells. Heilz observed in the calf, in the neighborhood of 

 an ovum surrounded by so-called primitive follicular epithelium, a group 

 of granulation cells, which so increased at that point where the ovum was 

 located that an excavation took place and, thereby, completely encom- 

 passed it. The granulation mass either already contained the ovum before 

 the development of a follicular cavity or else acquired this cavity after the 

 egg was completely surrounded. One of the foregoing conditions appears, 

 from these observations, to be the ordinary course in the calf. 



As soon as the follicle has acquired a certain size, it ruptures and dis- 

 charges the egg and the follicular fluid. There is still a division of opinion 

 as to the cause of the rupture of the follicle. It is highly probable that 

 there occurs a sudden augmentation of follicular liquid owing to vasomotor 

 irritation of the nerves and, consequently, a greater pressure on the part of 

 this fluid, along with f-imultaneous thinning of the follicular walls at that 

 part of the vesicle where it is to rupture. Holzl, on the other hand, com- 

 pares the rupture with that of the formation of an abcess, in that, between 

 the granular membrane and the thecafol iculi there occurs an important ac- 

 cumulation of migratory cells which form the so-called iheca folliculi interna. 



Under the pressure of this infiltrated cell mass, the contents of the follicle 

 are expelled in the direction of least resistance, that is, upon the external 

 surface. Zschokke holds a similar view, though he does not attribute the 

 rupture to the infiltration of the migratory cells, but to the multiplication 

 of the cells of the theca itself at the base of the follicle. From the 

 view-point of these two investigators, the thickening of the theca interna 

 at the base of the follicle and the thinning of the wall upon the surface of 

 the ovary has a special importance. However, it is essential to remember 

 that the unequal thickness of this membrane must be referred to the con- 

 dition of the blood supply since, indeed, the vessels become atrophied 

 in that part of the follicle where the rupture is to occur, and, hence, the 

 nutrition of this part of the theca becomes deficient. If now the mem- 

 brane increases in thickness on one side and decreases on the other, so will 

 the follicular contents be massed against the thin portion of the wall. The 

 rupture of the follicle, consequently, does not become inevitable except 

 there occurs a simultaneous increase of the intra-foUicular pressure and an 

 atrophy of the wall at the most prominent point, where it is to be ruptured. 

 If the latter were not the case, there would necessarily occur more or less 

 hemorrhage when the follicle breaks, which, however, Zschokke himself 

 denies for the cow. 



Against the Holzl-Zschokke view there is, first of all, the occurrence of 



