82 



pigments closely resembling the nat- 

 ural melanins. Studies of Hooker ^ on 

 cultures in vitro of frog mesenchyme 

 indicate that the pigment granules are 

 formed in the cytoplasm immediately 

 surrounding the nucleus, presumably 

 under the influence of oxidizing en- 

 zymes secreted by the latter. 



The nature of the differences be- 

 tween colors is still far from clear. 

 Onslow ^ could find no chemical dif- 

 ferences betAveen pigments extracted 

 from black and yellow rabbits and 

 considers that they differ merely 

 quantitatively. Most others do find 

 chemical differences as well as phys- 

 ical ones. Black pigment seems always 

 to be granular, while red may be either 

 granular or diffuse. Lloyd-Jones ® 

 found only granules in both intense 

 and dilute black pigeons, and found 

 red granules in red pigeons, but merely 

 a diffuse yellow in the dilute yellows. 

 The Davenports "^ found granules in 

 brown and black human hair, but 

 merely a diffuse color in auburn hair. 



There is a distinct difference in 

 solubility between the dark colors and 

 yellow. Miss Durham ^ found that 

 yellow granules in yellow mice dis- 

 solve quickly in potash, brown less 

 quickly, and black not at all. Gortner ^ 

 was able to separate two pigments in 

 black wool— one easily soluble in very 

 dilute alkali and also soluble in dilute 

 acids, while the other dissolved only 

 slowly in alkali and not at all in dilute 

 acids. This, of course, is a chemical 

 difference. The acid-soluble type was 



4 Hooker, D., 1915. Anat. Rec, 9: 393. 



5 Onslow, H., 1915. Proc. Roy. Soc, B-89: 

 36. 



^Lloyd-Jones, O., 1915. Jojtr. Exper. 

 ZooL, 18:453. 



7 Davenport, C. B. and G. C, 1909. Amer. 

 iVfl^, 43:193. 



8 Durham, F. M., 1904. Proc. Roy. Soc. 

 London, 74:310. 



9 Gortner, R. A., 1911. Biochem. Bull, 

 1:207. 



WRIGHT 



of protein nature. He considered it to 

 be a diffuse coloration of the keratin 

 structure, while he identified the in- 

 soluble type with the granules. In red 

 human hair he found only the acid- 

 soluble type. In brown horse hair and 

 black wool he found both, while in 

 brown and black human hair, black 

 rabbit hair and black feathers of do- 

 mestic poultry and crows he found 

 only the insoluble type. His two types 

 evidently correspond more or less 

 closely with yellow and black pig- 

 ment. This difference in solubility does 

 not necessarily indicate that yellow 

 and black are produced from different 

 chromogens. Indeed, Gortner has 

 shown that the insoluble type may be 

 produced from the soluble by treat- 

 ment with strong alkali. In a brief 

 paper in 1912, however, Gortner ^° 

 reports on a more fundamental differ- 

 ence between the insoluble melanin 

 from black feathers, black rabbit hair 

 and brown horse hair, and the soluble 

 melanin from black wool and brown 

 horse hair. The former yielded some 

 3% ash consisting largely of iron 

 oxide, while the latter yielded little or 

 no ash. This seems to demonstrate a 

 difference in chromogens in at least 

 these cases. But even here black pig- 

 ment may consist of a mixture of 

 melanins containing iron and melanins 

 which do not, derived perhaps from 

 the same chromogens as those which 

 under other conditions produce yel- 

 low. 



The chemical difference which 

 Gortner found suggests that the pres- 

 ence of iron bearing chromogens may 

 be the thing which is determined by 

 A4endelian factors for black as op- 

 posed to yellow. Such a view, how- 

 ever, is not in harmony^ with certain 

 other results. A4iss Durham ^^ found 



10 Gortner, R. A., 1912. Proc. Soc. Exp. 

 Biol, and Med., 9:3. 



11 Durham, F. M., he. cit. 



