iQii] Ross Aiken Gortner 213 



pigments which are insoluble in dilute acids. Neither do these 

 pigments correspond to the usual definition of melanin, i. e., soluble 

 in alkalis and insoluble in acids, for they are insoluble in dilute alkaii 

 and only by prolonged boiling with 0.2 per cent. sodium hydroxide 

 do some dissolve, while others resist this treatment and do not go 

 into Solution until a higher concentration of the alkaii is employed. 

 Apparently the melanin that occurs in the keratin structure is, in 

 these cases, insoluble in alkaline media and only after a certain 

 aniount of decomposition has taken place does Solution occur. 



There are, 'therefore, at least two typcs of melanin and these 

 occur in three combinations. In only one instance (auburn human 

 hair) have I found only the melano-protein. In black wool and in 

 pigmented horse hair both the melano-protein and an acid-insoluble 

 melanin are found, while in other keratin structures (see above) 

 only the acid-insoluble pigment is present. 



As to the cause of these differences, no data are, as yet, available. 

 It appears, however, very probable that we shall have to go back 

 to a modified form of a theory which has been long abandoned and 

 postulate that, in at least some instances, the melanin is dissolved in 

 the keratin or rather that a portion of the profein structure has 

 been so altered as to become deeply pigmented. Even if we grant 

 that the melanins are the product of an oxidase action, in no case 

 do we know the exact nature of the chromogen involved. In some 

 cases this chromogen may be relatively simple, and it may, indeed, 

 be only tyrosin, but there is no reason why this chromogen should 

 not be very complicated in other instances, even consisting of an 

 entire protein molecule. This being the case we should expect to 

 be able to isolate pigments which are a part of a protein residue, and 

 such pigments we find in the melano-proteins. These pigments 

 should not appear as granules, but rather as a diffused coloration of 

 the keratin and sluch a diffuse coloration is found in the case of 

 auburn human hair where no granules are to be observed (Daven- 

 port, 1909). The acid-insoluble pigments, on the other band, repre- 

 sent the pigment granules, which may be formed either by the oxida- 

 tion of a second chromogen, or by a further oxidation of the 

 melano-protein, whereby the pigmented portion of the molecule is 

 retained and broken off f rom the protein residue. To my mind the 



