180 



The Journal of Heredity 



certain dislinction could be observed 

 under the microscoiie between samples 

 of sepia and of black. When the same 

 dilution factor is introduced into reds, 

 the color is changed to yellow or cream, 

 and the sections show a marked reduc- 

 tion in the niunbcr of j^n^anules as com- 

 pared with red hair. With a still lower 

 {..'radc of im])erfect albinism, red is 

 wholly reduced to white, while black is 

 still only very slightly affected. This 

 greater susceptibility of red to the 

 influence of dilution factors is the rule 

 among mammals. 



MAGNIFIED HAIRS 



Longitudinal sections of guinea-pig hairs 

 magnified 1550 diameters. 



Fig. 1, Black hair; Fig. 2, red hair; Fig. 3, 

 yellow hair; Fig. 4, cream hair; CU, cuticle; 

 C, cortex; M, medulla; G, pigment granule. 

 (Fig. 10.) 



To these differences between black 

 and red may be added certain ones 

 observed by other workers. Miss Dur- 

 ham' found ■ a distinct difference in 

 solubilit\' of the ])igments. Dilute alkali 

 dissolxfd red i)igment easily btit black 

 hardly at all. (jortner- observed a 

 pronoiinccd chemical difference. Black 



pigment from several soiu'ccs contained 

 considerable iron, while red pignnent con- 

 tained virtually none. Onslow^ dis- 

 covered a difference in the enzjone 

 content of the skins of black and yellow 

 rabbits. He could extract a peroxidase 

 from the skins of black rabbits Init not 

 from yellow. With this ])eroxidase he 

 could ])roduce dark pigment resembling 

 melanin. 



At lirst sight it seems necessary to 

 suppose that black and red guinea pigs 

 differ from each other by many phy- 

 siological factors in order to account for 

 these many differences. But there is 

 ])robabl3^ only one primary physiological 

 dilference between black and red hair, 

 because a single genetic factor is enough 

 to effect the change. All the observed 

 differences are, in some way, direct or 

 indirect effects of this primary dfference. 



It is generally agreed that melanin 

 ])igment is produced by the oxidation, 

 through the influence of oxidizing en- 

 zymes, of protein metabolic products 

 such as tyrosin. The simplest ex])lana- 

 tion of the difference between black and 

 red hair seems to be that a certain 

 specific enzyme (enzyme II), which is 

 l^resent in black, is absent in red. This 

 enzyme increases the oxidizing power of 

 another, more fundamental, enzyme 

 (enzx'me 1) whose presence is necessary 

 for the i)roduction of any pigment. 

 (Wright.)'* The more thorough oxida- 

 tion of the chromogens in the case of 

 blacks is j^robably responsible for the 

 differences in color between black and 

 red hairs, the more thoroughly granular 

 nature, and the decreased solubility of' 

 black pignnent. 



The difference in iron content, noted 

 by Gortner, seems at first to indicate a 

 specific difference in the chromogens of 

 blacks and reds, as well as in the 

 enzymes producing them. BiU the 

 following exi)lanation is possible. The 

 chromogens oxidized in the red hair arc 

 also oxidized in black, but in addition 

 iron-containing chromogens are oxi- 

 dized in the latter. 



The presence of granular ])igment in 



9:3-4. 



» Durham, F. M., l'n)4. 

 !! Gortner, R. A., 1911. 



Pror. Row Soc London., 74:3lO-.S13. 

 Biorliou. Bull., 1:207-215. 1012. Proc. Soc. Exp. Biol. nn<l Med., 



2 Onslow, H., 1915. Proc. Roy. Soc, B-'-'9:36-58. 

 * Wright, S., 1917. Jour. Hkkkditv, 8:224-235. 



