U8 



THE AMERICAN NATURALIST [Vol. XL VI 



hut the chromogen only in small quantities. The results indi- 

 cate that the chromogen is formed slowly and used as formed. 



In the September number of the same journal 5 the same author 

 deals with the nature of dominant and recessive white. He 

 shows that, in so far as the presence or absence of pigment is 

 concerned, these two types of white, in certain mammals, are as 

 indistinguishable to the chemist as they are to the breeder. He 

 accepts the view that pigment is formed by the action of an 

 oxidase on a chromogen, and points out that dominant white 

 arises from the presence of a third body which prevents the reac- 

 tion between the oxidase and the chromogen. This might occur 

 in three ways: (1) the third substance, such as orcin, resorcin, 

 phloroglucin, or other substances of similar nature, may act on 

 the chromogen and thus prevent its oxidation; (2) it may itself 

 1"' oxidized by the tyrosinase, thus preventing action on the 

 chromogen; (3) it may act as a true anti-oxidase, and in some 

 manner inhibit the action of tyrosinase. 



The author gives abundant data to show that alternatives 1 

 and 2 are excluded in the cases with which he worked. Hence 

 the action must be of the third type— an inhibitory action. He 

 shows that dominant whites contain no pigment lacking in re- 

 eessives. He also shows that " aromatic compounds which carry 

 two hydroxyl groups in the meta position to each other are 

 capable of inhibiting the action of tyrosinase on tyrosin." If, 

 then, such a substance should occur in the animal body a domi- 

 nant white would result. Recessive white is presumably due to 

 the absence of either the chromogen or the oxidase, while at the 

 same time no inhibiting factor is present. From this it would 

 ;'l'l>< -ir that an albino might be dominant to color if it carried the 

 "l ii 'l m» I actor, yet it would require considerable work to dis- 

 ^lnguis i ^ etween such an albino and a true dominant white, 



allm^ic X an r t ^ e h 0ccurr ^ nc ^ of rec essive whites which are not 

 on^tvro/ eons ^ era ^ ons - Orcin inhibits the action of tyrosinase 

 ',v\ il^T \ !"• 1S ltS<1 ! " xi,lizcd h y a specific enzyme. If we 

 s\!viij'. nt , ' VI '" Sin< ' 1>y r - t . vn,si »<i*<' hy T, or.-in by 0, and the 

 S ^ x '] } . . n/y "" "' ,m " h " X1,ll/ -''* orcin by P, then an individual 

 ^ aimng only C and T would be colored, CTO would be white, 

 Certain PWfo^ "Studies on Melanin: III. The Inhibitory Action of 

 X V,'" - 7!!V' 1 S ' 1 l , ' st:i " ,1 ° s "P " Tyrosinase." Jour, of Biol.' Chem., Vol. 



