292 THE NITRIFYING BACTERIA 



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 ammonia 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 inocu- 

 lated with a few nitroso- or nitro-bacteria, energetic oxidation occurs, accom- 

 panied 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 ascertained 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 attract from carbon dioxide, in the absence of I i <//>(, 

 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 Wino- 

 gradsky, this carbonate 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 any means, has been converted into carbonates, and so withdrawn therefrom.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 atmo- 

 sphere that the carbon dioxide requisite for the construction of new cellular 

 substance is derived. He found that development did not occur in cultures con- 

 taining magnesium carbonate 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 require- 

 ments ash constituents apart of the nitrifying bacteria are satisfied. These 

 organisms will therefore be able to develop in places where there is nothing 

 present but bare rock, the cracks and fissures of which afford them a shelter 

 against the desiccating action of the winds. In fact, it was in such arid places 

 that A. MUNTZ (1.) constantly found nitrifying bacteria. It can very easily be 

 shown that friable (" rotten ") stone, especially that from the Faulhorn, is thickly 

 impregnated with these organisms. 



In order that the carbon of the carbon dioxide may be prepared for its 

 ultimate purpose, it must first be freed from the two attached atoms of oxygen. 

 In green plants the force requisite for this purpose is supplied by the thermal 

 power of the sun's rays ; but in the nitrifying bacteria, which also assimilate in 

 the dark, it is the energy liberated during the oxidation of nitrogen that effects 

 the dissociation of the carbon dioxide molecule. Consequently, the assimilation 

 of carbon is dependent on the oxidation of nitrogen, a fact quantitatively proved 

 by Winogradsky. According to this authority, about 35 mgrms. of nitrogen 

 are oxidised for each milligram of carbon assimilated, the atomic ratio being 



C : N = i : 30. 



More accurate knowledge of the progress of this assimilation especially 

 on the thermo-chemic-al side of the question is at present lacking. F. 

 HUEPPE (VIII.) and U. LOKW (V.) constructed equations to represent the 



