8 



The tyrosine bacteria belong to the genus Microspira created by Migula. 

 They are very small polar-monociliate, curved rodlets, somewhat varying in thick- 

 ness, mostly thinner than the cholera vibrios, which for the rest they resembly very 

 much. Like these they quickly liquefy broth gelatin and form on broth agar white, 

 vigorously growing soft masses. Sometimes they are united in long chains; the longest 

 individuals show distinct curves and remind of spirilli. If tyrosine is present in the 

 nutrient medium, many individuals take partly a black colour, swelling up very much 

 and sometimes becoming quite spherical, but the cilia do not become visible. They 

 produce indol, but do not give the nitrosoindol reaction. They grow well in peptone 

 solutions. 



The fresh-water form colours broth agar without tyrosine not or only very late, 

 but if tyrosine is added the brothagar grows rapidly black. The black-colouring 

 begins still earlier on the before 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 Microspira tyrosinatica 1 ). 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 labora- 

 tory 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 accor- 

 dance with the temperature and other culture conditions. If the corruption takes 

 place at room temperature 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 two or three weeks at 

 room temperature, they show deep brown spots evidently coloured by the same sub- 

 stance 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 2 ). It 

 is commonly but not always, a motionless organism, which can only develop on pep- 



') Migula 's Microspira nigricans, System d. Bakterien, Bd. II, p. 1013, does not 

 liquefy gelatin, but colours it brownish black. Whether tyrosine and tyrosinase occur 

 in this case has not been examined. 



*) Pigmentbildung bei Essigbakterien. Centralblatt f. Bakteriol. 2te Abt. Bd. 29. 

 S. 169, 1911. 



