CHAPTER XXXVI. 



THE NITRIFYING BACTERIA. 



203. The Recognition of Nitrification as a Physio- 

 logical Process. 



THE nitrogen excreted from the animal body as urea has not, when 

 converted into ammonium carbonate (see Chap, xxxii.), yet attained 

 the form in which it is usually taken up by plants. Although it 

 is indubitable that plants in general can obtain their requirements 

 of nitrogen from the ammonia salts, it is nevertheless certain 

 both as a result of manuring- experiments on the small scale and 

 also from the experience of agricultural practice that the majority 

 of cultivated plants absorb the element in question more rapidly 

 and abundantly when it is offered them in the form of nitrates. 

 In fact, for some of them, e.g. maize, buckwheat, and tobacco, 

 JUL. LEHMANN (I.) put forward the well-grounded assumption that 

 they derive their nitrogen exclusively from nitrates. Here again 

 Nature has made provision for the necessities of the case by con- 

 verting into nitrates the ammonia salts which partly as a result 

 of decomposition and partly as artificial manures find their way 

 into the soil. 



This process, long known, and briefly termed nitrification, was 

 defined in 1846 on the basis of an experiment by J. DUMAS (II.) 

 as a purely chemical process of oxidation. This observer re- 

 garded chalk as the intermediary facilitating the intimate com- 

 bination of ammonia and atmospheric oxygen. Fifteen years later 

 this role of " go-between " was ascribed by MILLON (I.) to the porous 

 humic bodies in the soil a view that still remained destitute of 

 any convincing proofs when revived in 1863 by BLONDEAU (II.). 



Ten years later other opinions began to arise. The first adverse 

 hypothesis was expounded in 1873 by ALEX. MULLER (I.), but 

 was not based on any solid foundation, nor was it followed up any 

 farther. Four years afterwards SCHLOESING and MUNTZ (I.), rely- 

 ing on the results of their researches in this direction, hazarded 

 the opinion that the formation of nitre in the soil is due to the 

 vital activity of organised ferments (soil bacteria). In a subsequent 

 communication these two workers detailed some of the conditions 

 requisite for the inception and course of nitrification. The opera- 

 tion is almost stagnant below 5 C., but becomes apparent at 12 C., 

 and attains its maximum at 37 C. As the temperature rises still 



375 



