935 
tyrosin is indeed formed, it is oxidised in another way but not to 
melanin. 
That this Sectnomyces must belong to another species than Acti- 
nomyces chromogenes, SO common in our environment, is obvious. The 
latter namely is characterised by the production of a dark brown 
pigment from pepton, (but not from tvrosin) in which, as I have 
formerly *) shown, under certain circumstances chinon may be found. 
Several other species of Actinomyces produce blue, red, or yellow 
pigments, whereby, as to the blue and red, the simultaneous presence 
of certain varieties of hay bacteria is favourable. In this case it is 
not tyrosin, but glucose, malates and nitrates that form the chromo- 
geneous food, so that the symbiose is then evidently associated with 
other factors than- those active in the production of melanin from 
tyrosin. 
Hitherto I have not yet been able in liquid cultures with the help 
of Actinomyces and its symbiont to produce a somewhat considerable 
quantity of melanin. This could not be foreseen as this genus is as 
common in the mud of moats and canals as in garden soil. But some 
experiments as the above to find our Actinomyces in mud gave no result, 
so it seems that this species at least is a real inhabitant of the soil. 
That pigment production in this case is difficult in liquid media, 
whereas Microspira tyrosimatica, which I described earlier ®), produces 
it as readily in liquid as in solid media, is perhaps owing to the 
general propriety of Actuwmyces to grow but slowly in solutions, 
probably in consequence of the little tension of the dissolved oxygen. 
Microspira, on the other hand, is as a true water microbe, evidently 
better adapted to that tension. 
Theory of the melanin formation *). 
In physiological chemistry it is generally accepted that at the tyrosin 
reaction from the tyrosin first originates homogentisinie acid, ammonia 
and carbonic acid after the formula 
C,H,,NO, + O, = C,H,O, + NH, + CO, 
Tyrosin Homogentisinicacid 
and that only afterwards by a new oxidation the homogentisinic 
acid is converted into melanin. 
1) Centralbl. f. Bakter. 2 Abt. Bd. 6. S 2, 1900. Arch Néerl. 1900, p. 327. 
Commonly the chinon is absent, which I did not know in 1900, 
2) These Proceedings, XIII, 1066. 
8) For the literature see Czapex, Biochemie der Pflanzen. Bd. 2, p. 462 and 478, 
1905. Aspernatpven, Physiologische Chem'e, p. 362 and 365, 1909, 
615 
