827 



Like many other changes in organic substances, these processes 

 are to day attributed directly or iudirectly to tlie physiological action 

 of microorganisms. He reviews the work of Frankland, VV^ariug- 

 ton, and Winogradsky, which leads to the conclusion that nitrifica- 

 tion is principally a physiological and not a purely chemical process. 

 With regard to the treeing of nitrogen in the processes of decay and 

 putrefaction, he briefly reviews the more recent work as follows : 



The experiments of J. Reiset and others lead to the general belief 

 that in the j)rocesses of decay, whether under exclusion or by free 

 access of air, the combined nitrogen is changed to tlu; elementary form. 

 But it is believed there are no chemical grounds for supposing that in 

 addition to ammonia free nitrogen also escapes when nitrogenous 

 organic material containing no nitrates or nitrites is allowed to decay 

 under exclusion of oxygen. In exact experiments by Kellner,* Tacke,t 

 and Ehrenberg,! these authors were not able to discover any genera- 

 tion of free nitrogen in the decay of nitrogenous organic matter, 

 whether in the presence of or under exclusion of oxygen. This result 

 was further verified by Schlosing§ in investigations on the marsh-gas 

 fermentation in barnyard manure. The case is different where nitrates 

 or nitrites are contained in or formed in the decaying material, for 

 experiments have shown that they suffer an energetic reduction. Tacke 

 found that in all decay in the presence of nitrates the latter were 

 reduced under formation of free nitrogen and all of the intermediate 

 stages of oxidation (N2O, XO, and ISTaOs). The relation of these prod- 

 ucts of reduction to one another showed wide variations, depending 

 largely on a number of circumstances. In Tacke's|| experiments the 

 decaying material was not well ventilated, and the author believes it 

 possible that in the j)resence of sufficient oxygen the reduction might 

 be altogether avoided. 



Leone ** studied the reduction of nitrates and nitrites by microorgan- 

 isms and sought to determine whether nitrates could be changed to 

 ammonia in the reduction. The results of his trials led him to believe 

 that the nitrogen of the nitrates is not assimilated by microorganisms 

 and is not changed to ammonia; only the oxygen of the nitrate and 

 nitrite is of importance to the life of these organisms. In a series of 

 experiments he was able to collect approximately the calculated amount 

 of nitrogen which was contained in the nitrate of soda emi)loyed. His 

 experiment indicated how extensive may be the generation of elementary 

 nitrogen in the reduction of nitrogen acids by microorganisms. 



*Zeitsch. f. physiol. Chem., 12 (1887), p. 95. 

 tLandw. Jahrb., 16 (1887), p. 917. 

 tZeitsch. f. physiol. Chem., 11 (1887), pp. 145, 438. 



§Compt. rend., 109 (1889), p. 835; Experimeut Station Record, vol. in, p. 736. 

 II Loc. cit. 

 ** Abs. in Centralbl. f. agr. Chem., 1890, p. 283. 



