( 1076 ) 
growth partly converted into a strong acid, probably gluconie acid. 
In presence of alcohol much acetic acid is formed. Consequently 
beer acidifies with great intensity. 
Solutions of 10 proc. glucose and 2 proc. peptone in tapwater 
with 10 proc. calcium carbonate at 25° or 30°C. grow black after 
a few weeks, the carbonate changing at the same time into calcium- 
oluconate. 
Although for the formation of the pigment the simultaneous 
presence of sugar and peptone is required, there is cause to admit 
that the pigment is an aromatic substance, taking rise from peptone 
alone, whereas this reaction only occurs during the growth of the 
microbe, for which growth also sugar is wanted. In an earlier paper 
I gave to such processes the name of auxobolisms. 
By the formation of the pigment in the gelatin plates the gelatin 
not only becomes deep brown, but at the same time quite insoluble 
in boiling water, which is the more remarkable as the newly 
isolated stocks of A. melanogenum liquefy the gelatin in the be- 
ginning (probably by the intense acid production and not by a 
specific enzyme). Older stocks lose this liquefying power, probably as 
they become slower in producing acid; their pigment formation, 
however, remains the same. 
Only very few substances render gelatin insoluble in boiling water 
as for example, formalin and chinon, whilst among the microbes, 
as far as known, only Actinomyces chromogenes (Streptothrie chro- 
mogena) has the same effect on gelatin by chinon production from 
peptone. As, moreover, the brown-coloured gelatin reduces silver 
in an ammoniacal solution of silver nitrate, and produces metallic 
mercury from an alkaline mercury solution, there is reason to admit 
that A. melanogenum does really produce chinon, this substance 
giving the same reactions. However the most characteristic reactions 
of chinon could not be obtained, namely, the blue-colouring of guajac 
emulsion and the production of iodium from hydroiodic acid. But 
the secretion product of the brown vinegar bacteria gives quite well 
the black-colouring with ferrisalts, also characteristic for chinon. 
SUNNY. 
The oxidation of chinic acid to protocatechetic acid is brought 
about by number of microbes beionging to very different groups and 
is easily demonstrated with ferrisalts. In particular Micrococcus 
calco-aceticus and some varieties of B. fluorescens non liquefaciens 
possess this faculty in a high degree and hence can be found and 
isolated from mixtures of bacteria. 
