THE ORIGIN OF THE DEFINITIVE OVA 27 



that this seems to be the case when relatively light oestrin 

 doses are injected (column 5), but not with heavy doses 

 (column 6). The theelin-injected animals received about 

 6.25 r.u. per day, and while continuous vaginal cornification 

 resulted, an apparently normal cycle of uterine changes 

 occurred and the ovaries appeared relatively unimpaired. 

 It is possible that in the animals receiving light doses the 

 ovogenesis inhibiting capacity of maturity hormones was 

 impaired but not the follicle stimulating capacity. The 

 heavier dosages may have caused the hydropic degeneration 

 of the germinal epitheUum described by Doisy, Curtis and 

 Collier (1931) and so prevented maximum ovogenesis, al- 

 though Swezy makes no note of such degeneration. Swezy, 

 noting that normally during the oestrus cycle there is a 

 drop in the production of new ova at the period just suc- 

 ceeding the period of maximum oestrin production (e.^., 

 ovulation), is inclined to attribute this drop (and therefore 

 the results in her oestrin-injected animals) to a factor other 

 than the ''suppression" of hormone secretion from the 

 pituitary. 



Recently Hisaw and his collaborators have advanced an 

 explanation of the oestrus rhythm which involves a sep- 

 aration of the maturity principle of the pituitary into two 

 hormones (Fevold, Hisaw and Creep, 1934; Lane and Hisaw, 

 1934; Hisaw, Fevold, Foster and Hellbaum, 1934; and Lane, 

 1935). One hormone is follicle stimulating, the other lutein- 

 izing and a chemical separation of the two has been attained 

 (Fevold, Hisaw and Leonard, 1931 ; Fevold and Hisaw, 1934). 

 These investigators report an increase in the total number 

 of follicles in rat ovaries on administration of follicle stim- 

 ulating hormone to prepubertal rats but no increase when 

 luteinizing hormone is administered. Their count of ''total 

 follicles" includes only ova in definitely formed follicles. 

 Swezy (19336) attributes the ovogenesis inhibition to the 

 luteinizing hormone. It is possible, therefore, that in addi- 

 tion to the ovogenetic activity which is independent of the 

 hypophysis {e.g.^ the ovogenesis seen in hypophysectomized 



