tone 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 growth partly converted into a strong acid, 

 probably gluconic acid. In presence of alcohol much acetic acid is formed. Conse- 

 quently 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-gluconate. 



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 sub- 

 stance, taking rise from peptone alone, whereas this reaction only occurs during 

 the growth of the rmcrobe, for which growth also sugar is wanted. In an earlier 

 paper I gave to such the name af auxobolisms. 



By the formation of the pigment in the gelatin plates the gelatin not only be- 

 comes 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 beginning (probably by the intense acid production and not by a specific 

 enzyme). Older stock 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 (Streptothrix chromogena) 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. 



Summary. 



The oxidation of chinic acid to protocatechetic acid is brought about by number 

 of microbes belonging to very different groups and is easily demonstrated with 

 ferrisalts. In particular Micrococcus calco-aceticus and some varieties of B. fluorescent 

 uon liquefaciens possess this faculty in a high degree and hence can be found and 

 isolated from mixtures of bacteria. 



The oxidation of quercite to pyrogallol is caused only by certain varieties of 

 Pseudomonas aromatica, so that we have here a very specialised function. Green- 

 malt extract allowed to grow aromatic by spontaneous corruption at low tempera- 

 ture abounds in that species and always contains numerous quercite bacteria which 

 besides, are fairly common in sewage and even in canal water as also in aromatic 



Melanine formation from tyrosine is proper to certain sea-vibrios and to Micro- 

 spira tyrosinatica not uncommon in sewage water and easily found by this reaction. 



