Melanin and its precursors I

According to Raper's hypothesis, the quinone of 5:6‐dihydroxy‐2:3‐dihydroindole‐2‐carboxylic acid is the red coloured precursor of melanin, obtained by the oxidation of tyrosine with tyrosinase. This paper deals with some derivatives of this “red substance”, the structure of which is still unknown, with phenylhydrazine and substituted phenylhydrazines. No reaction products could be isolated, however, with hydroxylamine, or with semicarbazide. In connection with observations of Jacobs and of Breijer attention is drawn to the fact, that the “red substance” may be of importance as an anti‐pernicious principle and that premelanin of the skin‐epidermis possibly plays a rôle in blood formation.