( 1075") 
mentioned culture medium, containing only tyrosine, although the 
growth on it is much slower than on brothagar. 
As nobody had ever before observed tyrosinase formation by bacteria, 
there is reason to consider these microbes as new for science; the 
species occurring in sewage water may be called Mcrospira 
tyrosinatica‘). It is an organism highly sensible to the nature of the 
nutrient substances, apt to lose the tyrosinase function by various 
not yet explained influences, but notwithstanding continuing for years 
in the laboratory as an hereditary constant species. 
§ 4. The brown pigment formed by the acetic bacterium 
Acetobacter’ melanogenum. 
When beer is left to corrupt at the air a film forms at the 
surface in which Saccharomyces Mycoderma and -acetic bacteria 
develop, or only the latter, in accordance with the temperature and 
other culture conditions. If the corruption takes place at room tem- 
perature it will be perceived, when the beer is contained in beaker- 
glasses, that after the film has closed over the surface, some of the 
beakers slowly assume a dark brown colour and after two or three 
weeks get so dark, that the beer seems coloured by caramel. 
For the isolation of the here active organisms streaks are to be 
made of the film on wort- or beer gelatin. Then these culture 
plates being kept fico or three weeks at room temperature, they show 
deep brown spots evidently coloured by the same substance which 
originated in the beer itself, spots in whose centre the colony of a 
vinegar bacterium is lying. As a matter of course the plates are 
further covered with colonies of Saccharomyces Mycoderma and of 
ordinary vinegar bacteria. 
Culture plates of 100 water, 10 gelatin, 2 peptone, 3 glucose, 
are also very good for growth and pigment production. The “brown” 
vinegar bacterium obtained in this way, I recently described under 
the name of Acetobacter melanogenum*s. It is commonly but not 
always, a motionless organism, which can only develop on peptone 
as source of nitrogen and produces the pigment from this substance, 
if at the same time glucose or maltose is present. Other nitrogen 
sources but peptone have not been found. The sugar is during the 
1) Miguta’s Microspira nigricans, System d. Bakteriën, Bd. Il, p. 1013, does not 
liquefy gelatin, but colours it brownish black. Whether tyrosine and tyrosinase 
occur in this case has not been examined. 
2) Pigmentbildung bei Essigbakterien. Centralblatt f. Bakteriol. 2te Abt. Bd. 29. 
S. 169, 1911. 
