that but one single species of microbes seems to exist, of which only some varieties 

 possess the faculty to form that substance. 



A more precise investigation showed that here the chemical reaction proceeds 

 quite correspondingly with the oxidation of chinic acid, but that the product is, after 

 all probability, pyrogallic acid, evidently resulting thus: 



C 6 H 12 O 3 + O = C 6 H 6 O 3 + 3 H 2 O 

 Quercite Pyrogallol 



Here, too, only one atom of oxygen per molecule of quercite is used. It should 

 be noticed that in these experiments a large portion of the quercite vanishes in 

 another way, probably as carbonic acid and water. 



The microbes causing this conversion are very generally distribued in our sur- 

 roundings, but although there occur among them a number of clearly distinct varieties, 

 they all belong to one and the same species, namely that of the aroma bacteria, 

 well known in milk and milk products and for the first time distinctly described by 

 Migula 1 ) as Pseudomonas aromatica. It is a polarmonociliate short rodlet, little 

 motile in plate cultures, more so in broth. 



The very dark colour of the pigment in an aerated alkaline medium makes it 

 easy to detect the quercite bacterium. If for example, on a broth agar plate with 

 0.5 proc. quercite, some drops of sewage water are spread, there is much chance 

 that after one or two days at 30 C. some colonies appear that are jet-black, or lie 

 amid a black diffusion field, distributed among the numerous non-pigment producing 

 colonies, which latter are little troublesome, excepting B. flnorescens liquefaciens, 

 whose secretion is injurious to the quercite bacteria. 



In a previous paper I alluded to a simple experiment whereby aromatic milk 



results 2 ). 



To this end milk should be kept at a relatively low temperature, for example at 

 15 to 20 C., with full admission of air, so that it is left to spontaneous corruption 

 by the aerobic germs it contains. The acidification is at first feeble on account of 

 the low temperature, but it is then the aroma bacteria increase very much and 

 produce the characteristic ester which has not yet been nearer examined. 



If of such aromatic milk streaks are made on a quercite plate of the above com- 

 position a large number of brown colonies of quercite bacteria appear after 2 X 24 

 hours at 30 C. An examination of their faculty of producing the aroma in milk 



*) System der Bakterien, Bd. 2, p. 880, 1900; with fig. Bd. I, Tab. i, fig. 8. This 

 description is based on Bacillus crassus aromaticus Tataroff. Probable synonyms: 

 B. aromaticus lactis Grimmer, Centralbl. f. Bacteriol. 2te Abt., Bd. 8, S. 584, 1902.- 

 .B. butyri aromafaciens Keith, Bacillus N. 41 Conn; Pseudomonas fragariae Gruber ( 

 Centralbl. f. Bact.' 2te Abt. Bd. 9, p. 705, 1902. - - Ps. fragariae Gruber, Id. Bd. 14, 

 p. 122, 1905, - - and Ps. fragaroidea Harald Hussld. Bd. 19, p. 661, 1907. - - Perhaps 

 likewise the yellow-coloured Ps. trifolii of Harald Huss, Id. Bd. 19, p. 68 and 149, 

 1907, and several other different forms less easily recognisable in the literature are 

 synonyms. Bacillus esterificans Maassen, Arbeiten des Kais. Gesundheitamtes, Bd. 15, 

 1899, is Quite another species, producing spores and belonging to the hay bacilli, and 

 thus related with Granulobacter polymyxa Prazmowski. 



2 ) Fermentation lactique dans,le lait. Archives Neerlandaises, Ser. II. T. 13. p. 350. 

 1907. 



