C. H. Danforth 261 



operations that in their effects on plumage Leghorn and Sebright testes are 

 interchangeable; and Danforth and Foster'^ found by transplantation of skin 

 that the differential factors involved actually reside in the skin itself, presum- 

 ably in the feather follicles. Two pieces of skin healed together and growing 

 adjacent to each other on the same host will, if one is hh the other HH, pro- 

 duce feathers respectively of the cocky and henny type. This observation was 

 substantiated by Champy'^ who transplanted skin of a Phoenix cock to a 

 Sebright and got typical male plumes surrounded by the henny feathers of 

 the host. Nevertheless, as late as 1936, when Callow and Parkes" failed to get 

 a response in the plumage of Sebright capons injected with androsterone, it 

 was again suggested that henny plumage of the Sebright cock must be due 

 to another substance secreted by the testis, "probably oestrin." Later experi- 

 ments with other androgens have caused this opinion to be revised. 



Gallagher, Domm and Koch,^ and Danforth" next showed that extracts 

 from bull testes would "feminize" the plumage of Sebright capons, and the 

 latter also found that an ordinarily subthreshold dose of the extract could be 

 made to supplement a hitherto inadequate output of a testicular fragment. 

 Perhaps even more interesting was the demonstration, which has been re- 

 peated in connection with the present experiments, that the comb, "psyche," 

 and feather follicles have different threshold levels, the level for the latter 

 being appreciably higher. Taking advantage of this fact one can, by incom- 

 plete castration or injection of sufficiently small amounts of testosterone into 

 capons, convert genetically HH birds into phenocopies of the hh form that 

 would be likely to deceive even a critical observer. 



Transplantation of avian testes, and injection of extracts from testes of 

 mammals, is not entirely satisfactory, however, since the composition of the 

 extracted hormones is at least somewhat uncertain and there is also the possi- 

 bility that the effects observed may be mediated indirectly through some 

 other gland. The latter possibility is mentioned again and again in the litera- 

 ture, particularly with reference to the thyroid. Since the discovery by Torrey 

 and Horning^'-' of the effect of desiccated thyroid on plumage the question 

 has been discussed, pro and con, by Crew;^ Danforth;"^ Parkes and Selye;"' 

 Emmens and Parkes;"" and Chu."" The relation of hypophysial and suprarenal 

 secretions to plumage types is still less well known. Various aspects of their 

 possible relations have been considered by Danforth;'"'^ Hill and Parkes;"® 

 and Witschi.^ A survey of this literature, which need not be undertaken here, 

 makes it apparent that with the partial exception of those on the thyroid and 

 ovary the experimental studies thus far have not sufficed to differentiate be- 

 tween the direct and indirect effects of the rather numerous hormones which 

 show evidence of playing some role in the determination of plumage character- 

 istics. In an attempt to meet this objection in the case of testosterone the 

 synthetic drug* was administered in various ways to Sebright capons. 



* The writer is indebted to the Sthering and Ciba firms for generous supplies of testosterone 

 propionate made up in tire desired vehicles. 



