332 OSCAR RIDDLE. 



adding the tyrosin ; an adequate account of the history or 

 nature of color changes in such a solution seems hardly possible 

 since as Table I. shows much of melanin production results in 

 colors which are paler than red and the origin of all these, and to 

 some extent the final color, would be obscured by the initial 

 presence of red. Miss Durham was unable to state exactly 

 what the extracts of the albino skins were capable of doing, but 

 thought they probably contained no such enzymes. 



The factor hypothesis of Castle avoids some of the pitfalls of 

 the earlier theory, but seems to rest on essentially the same base. 

 It is necessary to examine in detail the statements and conclusions 

 in Cuenot's paper. 



Cuenot says : " There should be, however, in this case either 

 two different chromogens and only one enzyme, or only one 

 chromogen and two enzymes, the one for the blackish, the other 

 for the yellow pigment." The facts of the origin of melanin do 

 not substantiate Cuenot's hypothesis because the colors do not 

 form on this plan ; one and the same chromogen is known to 

 form yellow and black ; one and the same ferment tyrosinase 

 -is known to produce both yellow and black from the same 

 chromogen. 



According to Cuenot : "The germ plasma of the gray mouse 

 (black and yellow pigment) should contain potentially the three 

 substances which, by their reciprocal reactions, later produce the 

 deposition of pigment in the hair ; and doubtless these three sub- 

 stances are contained in the potential state within many of the 

 material particles of the germ plasma (representative particles, 

 mnemons, etc.)." But three such substances are not required 

 for the production of black and yellow ; these two color com- 

 pounds are known to be but different stages of oxidation of the 

 same substance. Furthermore, the locating of all the factors which 

 determine the development of these colors in the germ plasm 

 does not reckon with the facts of color physiology already cited. 



Continuing, Cuenot says : " In a gray mouse (black and yellow 

 pigmented) there are three mnemons, one for the chromogen, 

 and two for the two enzymes ; in a black mouse there are only 

 two mnemons, one for the chromogen and another for the forma- 

 tive enzyme of black pigment." Statements made above furnish 

 a sufficient refutation of this conception of Cuenot's. 



