ASSIMILATION IN THE DARK. 381 



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 (I.) constantly found nitrifying bacteria. 

 It can very easily be shown that friable ("rotten") stone, especi- 

 ally 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 pur- 

 pose 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 m.grms. of nitrogen are oxidised for each milli- 

 gram of carbon assimilated, the atomic ratio being 



C : N = i : 30. 



More accurate knowledge of the progress of this assimilation 

 especially on the thermo-chemical side of the question is at pre- 

 sent lacking. K HUEPPE (VIII.) and 0. LOEW (V.) constructed 

 equations to represent the changes occurring in the reaction, but 

 these can merely be alluded to here. Godlewski ascertained that 

 by no means the whole of the ammoniacal nitrogen eliminated 

 during the nitrification is recovered as nitrous or nitric acid, but 

 that a portion is liberated in its elementary condition, and escapes 

 from the solution undergoing nitrification. It may be opined that 

 this loss is not immediately connected with the action of the nitri- 

 fying bacteria, but is only an associated phenomenon produced 

 by the reaction of the N ? 3 on the still undecomposed NH 3 , in 

 accordance with the equation 



The reason for this is that the nitrous acid liberated does not in 

 every part of the liquid come into immediate contact with the car- 

 bonate which would protect it from the action of the ammonia. 



208. Wall-Saltpetre and Plantation-Saltpetre. 



The particulars already given of the life-conditions of the 

 nitrifying bacteria will explain the origin of wall- saltpetre, i.e. the 

 corroding efflorescence of saltpetre on masonry. This substance is 

 a white snow-like mass, consisting principally of crystals of calcium 

 nitrate, and occurring with particular frequency on the walls of 

 stables and closets. It is precisely in such places that the fission 

 fungi under discussion find an abundance of the food-stuffs they 

 require : the ammonia salt is supplied by the urea absorbed by and 



