MELANIN COLOR FORMATION. 337 



for brffivn, chocolate, red, yellow, etc. (more accurately, an enzyme 

 for each step of oxidation from tyrosin to black melanin), without 

 the absence of a single one. If there be introduced here the primal 

 Mendelian conception of the freedom of each of these factors to 

 be distributed in gametogenesis according to the laws of chance, 

 how often then may we expect pure-bred black parents to produce 

 black offspring? 1 



There are reasons, derived from our general knowledge of 

 oxidizing enzymes, why this assumption of high tyrosinase 

 specificity is highly improbable and some evidence against this 

 position has been cited from Gessard and Bertrand ; a direct 

 refutation of it is furnished by the experiments of Tornier. He 

 showed that he could take animals which would have, according 

 to Mendelian assumption, the enzyme for " black," and make 

 them produce any one of three or four of the less oxidized mem- 

 bers of the color series ; these same forms could again under other 

 conditions be made to produce the more highly oxidized black, 

 etc. Obviously, the presence of a black-producing enzyme did 

 not determine the color here ; but conditions of life did so deter- 

 mine. The further assumption of inhibiting factors ready at all 

 points of color-production to account for lower grades of color 

 formation, and all other secondary assumptions to support the 

 primary one are clearly unnecessary, and since a clearer, saner 

 interpretation is possible they need not be considered. 



'This would be the usual or expected type of specificity if such thing should exist. 

 I call attention to its implications merely to forestall any further thought regard- 

 ing its possibility. The sort of specificity of enzymes that has thus far been 

 assumed by the Mendelians has, however, been of a different sort ; namely, that for 

 the production of each color only one enzyme is necessary, but the enzyme which 

 produces any particular color is specifically different from those which produce other 

 colors; the case is not really different from an assumption that pepsin is specifically 

 different in different, but closely related races and varieties. Unlike the case cited 

 above, here each germ possesses only one or two zymogens, each capable of super- 

 vising the complete production of some one color, and therefore all the offspring 

 could (in contrast to above) be provided with color. The only evidence that has been 

 adduced for this sort of specificity is the rather incomplete and unsatisfactory results of 

 Miss Durham already cited. All else has been mere assumption on the part of the 

 Mendelians. But this type of specificity becomes a very unusual and extraordinary 

 thing as soon as we find that all of the colors form in a continuous oxidation series. 

 To cover this fact the assumption is obligatory that in melanin production, six, ten or 

 a dozen tyrosin oxidizing enzymes are concerned ; that these are all able to take the 

 first steps of tyrosin oxidation ; that they are differentiated merely by their " strength," 

 that is, the extent to which they can carry the oxidations. 



