GONADS AND THE PITUITARY BODY 



cannot be answered until pure gonadotropic hormones are 

 available for assay by the various methods. It is safer to as- 

 sume that results obtained by one method cannot be com- 

 pared with those secured by another; qualitative or quantita- 

 tive differences which may be found — especially if the ani- 

 mals used belong to different classes or if different methods of 

 administration are employed — may or may not be of im- 

 portance in establishing the production of identical or differ- 

 ent effects. Some of the factors which may affect assays in 

 the mouse and rat are probably also of importance in the per- 

 formance of assays with other animals; these factors are dis- 

 cussed in section 4 below. 



T . The production of ovulation in the toad. — Bellerby (1933) 

 studied some of the conditions affecting the assay of gonado- 

 tropic hormone by the production of ovulation in the toad 

 {Xenopus laevis). Temperature appeared chiefly to affect the 

 rapidity of the response. He recommended that quantitative 

 assay, by the administration of the same dose of extract to a 

 large enough group of toads, each of about the same weight 

 (35 g.), be based upon the percentage of toads in which 

 ovulation occurred. If ovulation was produced in 50 per cent 

 of a group of toads, a "unit" was the dose administered to each 

 toad. The method appears to be sensitive (i kg. of fresh pars 

 glandularis of the ox was found to contain 750 "toad-units"), 



2. The stimulation of the growth of the immature pigeon s 

 testis. — Following Riddle's report (1931), Evans and Simpson 

 (1934) estimated the approximate amount of gonadotropic 

 hormone by its stimulating effect on the growth of the imma- 

 ture pigeon's testis. According to Evans and Simpson this 

 testicular response is useful not only because of its sensitivity 

 (greater than that of the ovary of the immature rat) but also 

 because of its specificity. Unlike the other three methods by 

 which effects are observed by gonadotropic extracts not ob- 

 tained from the pars glandularis (e.g., prolan), precocious 

 growth of the immature pigeon's testis is caused only infre- 



[169] 



