^97 



Microbiology. — "(Icidation of mamjanocarhondti' In/ nncroJ)i's'\ 

 By Piof. Dr. M. W. Hki.ikhinck. 



Ill experiments on nitriticatioii, ituinmanocarbonate being used as 

 indicator of oxidation, it was found that the nitrifying microbes 

 themselves could not attack this substance, but that other organisms 

 possess this power in a high degree. 



When two pieces of filter paper, with a little iiianganocarboiiate 

 between them and moistened with a dihite solution of ammonium- 

 chloride and kaliumfosfate, are infected with garden soil and kept 

 at about 25° C, dark brown or black s))ots of a manganicompound 

 will appear upon them after some days. 



The reactions characteristic of the thus produced manganicom- 

 pound, are the sudden decomposition of liydrogenperoxide and the 

 oxidation of hj'droiodic acid under secretion of iodium, which reactions 

 are not caused by the manganocarbonate itself. 



In the microscopic tield tlie newly formed manganicom[)Ound 

 is sometimes precipitated as a detritus, in other cases in the shape 

 of black sferites, no doubt chiefly consisting of Mn^O., or MnO^. 



When examining the related microbes, bacteria and various species 

 of mould were recognised as cause of tliis oxidation. 



The best way to obtain these organisms in a form fit for further 

 experiments, proved to be the sowing of the material, developed on 

 the filter paper, on plates obtained by dissolving agar in water to 

 which, likewise as to the filter paper, had been added, besides 

 c.a. 17o manganocarbonate, 0,057o kaliumfosfate and 0.057n ammo- 

 niumchloride or. as much nitrate. With an equable distribution of the 

 carbonate such plates are as white as paper. When cultivating there- 

 on the oxidising microbes, the bacteria form a deep brown granuious 

 deposit, partly at the glass wall, whilst the mould species produce 

 large black spots, whereby in the agar black sferites are formed, 

 which will sometimes grow out to Vio millimeter diameter and are 

 then visible to the naked eye. 



As to the bacteria, the manganicompound mostly remains dif- 

 fusedly precipitated in the extensive colonies, without producing 

 distinct sferites. 



It is true that in these brown spots, which after some weeks 

 attain one or two cm. in diameter, small grains are found, but 

 these prove to consist of cluui[>s of bacteria, enclosed in a brown 

 or black envelope or film of manganioxides. The capsulated bacteria 

 ha\e the shape of veiy (hin, short rodlets -, the loose ones, occui-riiig 

 in the same spots, that of micrococci. 



