18 SELMAN A. WAKSMAN 



The pigment production is usually ascribed to an enzyme 

 tyrosinase, which is able to convert tyrosin into dark colored 

 melanins. Beijerinck (1913) has shown, however, that tyrosin 

 is oxidized into melanin only by a symbiotic action of an Actino- 

 myces with a common soil bacterium; neither . organism alone 

 can oxidize the tyrosin to the same stage. Attention was called 

 in the previous experiments to the fact that many species of 

 Actinomyces produce a yellow brown to dark brown soluble 

 pigment even on media that do not contain any tyrosin. We 

 must therefore conclude that the brown pigment produced by 

 certain species on organic media is due not only to the melanins 

 produced from tyrosin, but also to some other substances pro- 

 duced from amino acids besides tyrosin and from the sources of 

 carbon. 



A number of species were inoculated upon an alkaline tyrosin 

 agar (Krainsky, 1914) and only A. scabies and no. 205 produced 

 a soluble brown pigment. All the other species made a good 

 growth upon this medium, but produced no soluble pigment. 

 If, as Beijerinck (1913) stated, tyrosinase is a mixture of two 

 oxidizing enzymes, one converting tyrosin into homogentisic 

 acid and the other oxidizing the acid to melanin, then out of all 

 the species studied, only A. scabies and no. 205 are able to pro- 

 duce both of these enzymes together. Out of four strains of 

 A. scabies obtained from different sources, only two gave the 

 tyrosinase reaction, these two being the more vigorous growers. 

 The experiment on the utilization of tyrosin and on the produc- 

 tion of a brown to black soluble pigment was repeated again in 

 solution. A medium was made up containing the same con- 

 stituents as the synthetic solution used (Czapek's) except that the 

 NaN0 3 was replaced by 0.1 per cent of tyrosin and the sucrose 

 by 3 per cent glycerol. The medium was tubed, sterilized, 

 inoculated and incubated at 25° for fifteen days. The results 

 are presented in table 3. 



The previous results are confirmed; not all the species that are 

 able to produce a brown to black soluble pigment on gelatin, 

 potato plug and synthetic media containing organic substances, 

 particularly proteins and peptones, are able to produce a soluble 



