Regenerative Capacity of Ovarian Tissue 45 



is the same "whether the damage is caused physiologically 

 (from unknown factors) or artificially (by X-rays)", and on 

 the basis of estimates of the total number of normal oocytes, 

 and the percentage of oocytes regarded as atretic, the fol- 

 lowing function 



t n = a(l - r) n 



in which t n = the number of oocytes after n periods of atresia; 

 a = the original number of oocytes; and r the percentage of 

 atresia, is used to show that the ovaries would be practically 

 exhausted within two years if new oocytes were not formed; 

 consequently, oogenesis must occur in the mature ovary, two 

 years being the theoretical maximum life of the oocyte. 



Once again both facts and arguments are hardly adequate 

 to support the conclusion. In the first instance, Van-Eck 

 assumes that normally "atresia is of short duration for the 

 primordial and small primary follicles — the follicle is resorbed, 

 leaving no trace, and its place in the ovary replaced with 

 stroma." To the best of my knowledge this contention is 

 arbitrary, in so far as no critical proof has ever been provided 

 that under physiological conditions atresia of young oocytes 

 is a rapid process. Estimates of the rate of atresia, inferred 

 from observations on single ovarian phases, are just as insecure 

 as are inferences of postpubertal oogenesis from a picture 

 of an epithelial cord apparently budded from the germinal 

 epithelium. No-one knows how long an atretic oocyte or 

 follicle in a normal ovary can remain in the same apparent 

 state; nor indeed is there any agreement among students 

 about the occurrence of a high rate of degeneration in prim- 

 ordial oocytes. 



A second weakness of the work is that it assumes that 

 atretic oocytes can be diagnosed sufficiently well to justify 

 statements such as: "the percentage of atretic ova was 

 constant for each group ". (According to her estimates 4 • 5 per 

 cent of all oocytes are atretic or in process of becoming so.) 

 Elsewhere in the paper, however, she noted that "for the 

 primordial oocytes it is sometimes difficult to determine 



