Abstract of a communication on nitrification. 



made in the meeting of the „Wis- en Natuurkundige Afd. der Kon. Akademie v. Wetenschap- 

 pen, Amsterdam" on June 25, 1892. Nature, London, Vol. 46, 1892, p. 264. Een verkort 

 verslag hiervan is te vinden in: Verslagen Kon. Akademie van Wetenschappen, Wis- en 

 Natuurkundige Afd., Amsterdam, Deel I, 1892, blz. 14. 



M. Beijerinck spoke of the culture of organisms of nitrification on agar- 

 agar and on gelatin. First it was stated, in accordance with the discovery of W a- 

 r i n g t o n and \V i n o g r a d s k y, that nitrification consists in two processes 



— the formation of nitrous acid from the ammonsalt by a specific bacterium and the 

 oxidation of the nitrite into nitrate by another and independent species of bac- 

 terium. Secondly, that both these processes occur only when soluble organic matter 

 is reduced to a minimum such as has been proved by the classic researches of W i- 

 nogradsky and the Franklands. Even 0. 1 %, of calcium-acetate retards 

 nitrification strongly. Thirdly, it was found that organic matter in the solid state 

 does not in the least interrupt or retard nitrification. Therefore an attempt was made 



— and successfully — to cultivate the nitrous and nitric bacteria on agar-agar, fuUy 

 extracted with distilled water and afterwards boiled with the inorganic salts needed 

 for nitrification. If with these salts some pure precipitated carbonate of lime was 

 added to the agar it was possible to obtain a „chalk-agar-plate", whereon the ni- 

 trous bacteria of the soil, after their growth into colonies, could directly be numbered. 

 For this purpose the chalk-agar is poured into a glass-box, and some soil suspended 

 in sterilised water brought on the surface of the solidified plate. After three to four 

 weeks the colonies become visible as the centres of clear. transparent, perfectly circu- 

 lar diffusion figures, formed by the solution of the carbonate of lime in the nitrous 

 acid, the very soluble calcium-nitrite diffusing in all directions in the agar-plate. In 

 this way it was found, for example, that out of ca. 1 millogrammes soil taken from 

 under a sod of white clover in a garden at Delft, thirty colonies of the nitrous bac- 

 terium could be cultivated. The species is the same as that described as the Eu- 

 ropean form by W i n o g r a d s ky, growing, as well as zoogloea, quite free, and 

 possessing the form of a small, moveable mikrokok with one cilium. Gelatin, pre- 

 pared with the same precautions as the agar, can also be used, but therein the produc- 

 tion of nitrous acid soon ceases. The nitrous bacterium does not liquefy the gelatin. 

 Though it does not grow or oxidize when organic matter is present, it does not lose 

 these powers by this contact, as shown when brought anew under adequate con- 

 ditions. The nitric bacterium was also isolated on fully extracted agar, to which 

 0.1% potassium-nitrite and some phosphate was added. The colonies are very small 

 and coloured light yellow. They consist of very small non-moving mikxokoks or short 

 ellipsoids. They lose their power of oxidizing nitrites by the contact of soluble 



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