238 



The Journal of Heredity 



B, Au, R, Br, Y, and W stand for black, auburn, red, brown, yellow and white hair respectively 



(B) (Br) and (Alb) stand for black, brown and all)in()tic eyes. 



Instead of supposing that the factors 

 l)v which hlack differs from red deter- 

 niino the presence of a grantilar pig- 

 ment wholly independent of a red. we 

 suppose tliat an additional enzyme 

 (enzyme II) is determined which con- 

 verts the fundamental enzyme, which 

 alone produces red, to an enzyme which 

 can produce black. The same effect is 

 supposed to take place in the eyes and 

 skin as in the hair. The change from 

 white or flaxen to red is interpreted as 

 being due to an increase in the funda- 

 mental enzyme (enzyme 1) instead of 

 the addition of diffuse red pigment 

 wholly independent of black. As in the 

 other mammals, we suppose the thresh- 

 old for production of red (enzyme I 

 acting alone) is at so nuich higher a 

 level than the threshold for hlack 

 (enzyme I assisted by enzynu' 11 ) that 

 we find white or flaxen in place of red 

 at a level at which we lind black virtti- 

 ally unchanged. 



We would expect to lind elYects of 

 the factors 2a., on the skin as well as 

 in hair and eyes. The general correla- 

 tion has been alluded to. In the case 

 of red. Pearson has shown that freck- 

 ling is especially characteristic of red 

 haired persons. 



ALIUNISM, BLOXDNESS, ANO KF.I) HAIR 



The question now arises as to the 

 position of albinism in this scheme. If 

 we take the condition of the eyes— pale 

 iris, red puj)il. nystagmus, photo- 

 phobia, and poor vision — as the fimda- 

 mental criterion for albinism in man 

 (rather than mere white hair), we see 



that such a condition may be reached 

 by extreme variation along two routes. 

 Extreme reduction of enzyme I should 

 at length reduce the blue eyed black- 

 haired t}pe to a pale brown or even white 

 with albinotic eyes. comparal)le to the 

 albinos of rodents. Doubtless most of 

 the albinos of dark races are of this 

 type since the chances are that such a 

 rare variation differs from the normal 

 by only one factor. The evidence on 

 llic whole indicates that such albiiiism 

 behaves as a tmit recessive factor. Such 

 albinism dotibtless also exists in the 

 while race, but is not easy to distinguish 

 from the second kind. The second kind 

 of albinism we find in Pearson's red 

 and yellow haired albinos which sug- 

 gest extreme reduction of enzyme II, 

 rather than of enzyme 1. 



'J'hese red and yellow haired albinos, 

 however, appear to be very tmcomuion. 

 lUit the observation of Davenport and 

 Pearson in regard to the unusual fre- 

 c[tiency of red haired persons among 

 the relatives of albinos of the ordinary 

 white haired kind suggests tiiat we are 

 here dealing with the combined eifects 

 of both kinds of variations. Thus 

 variations of class 2a.j. which alone 

 may reduce black merely to a blue eyed 

 red, only a little more extreme than 

 tisual. when associated with a grade of 

 general dilution which will reduce red 

 to white, but black eyed l)lack morel\- 

 to blue eyed black, should result in a 

 blue eyed white type with more or less 

 albinotic eyes. Such an albino would 

 be closely comparable with the red- 

 eyed white guinea-pigs (sec CrCr\ 



