380 THE NITRIFYING BACTERIA. 



207. Assimilation in the Dark. 



The incapacity (recorded in 204) of the nitrifying bacteria 

 to grow on nutrient gelatin is, in the main, attributable to their 

 general distaste for organic nutriment, a peculiarity noted by 

 MUNRO (I.) in 1886. The smaller the quantity of organic food 

 present, the more energetically do growth and oxidation proceed ; 

 and the latter effect is most powerful in solutions containing 

 exclusively inorganic matters. For nitroso-bacteria Winogradsky 

 recommends a mixture of 2-2.5 grams of ammonium sulphate, 

 2 grams of common salt, and a sufficient quantity of magnesium 

 carbonate per litre of well-water. For nitro-bacteria the ammonia 

 salt is replaced by sodium nitrite. 



When such a nutrient solution containing solely inorganic 

 matters is inoculated with a few nitroso- or nitro-bacteria, energetic 

 oxidation occurs, accompanied as was first brought into notice by 

 W. HERAEUS (I.) in 1886 by a rapid reproduction of the bacteria. 

 When development is concluded, and the available quantity of 

 ammonia or nitrite oxidised, then the bacterium crop grown in 

 this manner contains a certain quantity of organic matter, the 

 carbon of which has been exclusively derived from inorganic 

 sources in this case carbon dioxide. The amount was ascer- 

 tained by Winogradsky, by four quantitative analyses, as 0.020- 

 0.022 gram per 100 c.c. of liquid. Consequently the nitroso- and 

 nitro-bacteria are able to abstract from carbon dioxide, in the 

 absence of tight, the carbon necessary for the construction of 

 their cells, and are therefore able to assimilate carbon dioxide 

 in the dark. 



Two sources of carbon dioxide are available to the nitrifying 

 bacteria. One of them is the carbonate present in the nutrient 

 solution (or soil), and which is also necessary for other reasons 

 already given in 204. According to Winogradsky, this car- 

 bonate supplies carbon to the newly-formed bacteria, which are 

 assumed to decompose it by means of the acids they produce, and 

 then utilise the carbon in the construction of new cells. He 

 considers that the function of these organisms is to liberate and 

 restore into general circulation the carbon that, by any means, 

 has been converted into carbonates, and so withdrawn therefrom. 

 On the other hand, E. GODLEWSKI (I.) showed that it is chiefly 

 from the atmosphere that the carbon dioxide requisite for the 

 construction of new cellular substance is derived. He found that 

 development did not occur in cultures containing magnesium car- 

 bonate when only air free from carbon dioxide was admitted. 

 Now the atmosphere contains not only carbon dioxide, oxygen, 

 and water, but also ammonium carbonate, with which substances 

 the nutrient requirements ash constituents apart of the nitri- 

 fying bacteria are satisfied. These organisms will therefore be 

 able to develop in places where there is nothing present but bare 



