THE NITRIC FERMENT. 209 



by the intervention of the butyric ferment and of analogous 

 secondary ferments. 1 



Their action is exerted between determinate limits of 

 temperature. Below 5 it is inappreciable, becoming appreciable 

 at 12. It becomes more and more active as the temperature 

 rises to about 37, at which temperature the nitrification is ten 

 times more rapid than at 14, though still rather slow, all the 

 other conditions moreover being the same. Beyond this it 

 grows slower; at about 45 it is less active than at 15, and 

 ceases completely at 55. 



According as the temperature rises, and especially if it be 

 brought to 100, the vitality of the corpuscles diminishes, so 

 that mould or water in course of nitrification loses this property 

 without recovering it after cooling. They also perish under the 

 influence of the vapours of chloroform and antiseptics. 



Moisture is indispensable to them. It is even sufficient to 

 dry in the air a fertile piece of mould for it to become sterile 

 after a time. The corpuscles do not support a prolonged 

 privation of oxygen, at least when operated upon in a liquid. 



They act equally well in the dark or under the influence of 

 a moderate light, but a strong light is prejudicial to them. 



Their action requires the aid of a slight alkalinity, due 

 either to the presence of calcium carbonate, or to that of two to 

 three thousandth parts of alkaline carbonates. Beyond this 

 degree alkalinity injures them, which accounts for the un- 

 favourable influence exerted by liming upon nitrification. The 

 development of the nitric ferment in water requires the 

 simultaneous presence of an organic substance and a nitrogenous 

 compound. But the ratio between the carbonic acid and the 

 nitric acid produced is in no way constant. It is the same with 

 the absorption of oxygen, which is continually going on at the 

 expense of a soil which has been rendered sterile by a tempera- 

 ture of 100 or by the action of chloroform vapours. 



The nitric ferment is multiplied by sowing a nourishing 

 liquid, or earth, with a small piece of arable soil or a few 

 cub. cms. of sewage. It does not generally exist in the dust in 

 the air. Its multiplication is slow, and seems to be effected by 

 budding. The existence or absence of porous bodies appears to 

 have very little to do with nitrification, contrary to the views 

 formerly held. 



Ordinary mould and mycoderms are quite distinct from this 

 ferment, and even contrary to its action. In fact, they destroy 



1 Dehe rainet Maquenne, " Comptes rendus," torn. xcv. p. 691 ; Gayen, 

 same collection, torn. xcv. p. 1365. These auxiliary ferments, or rather 

 perturbators, reduce inversely the nitrates with production of nitrites, 

 nitrogen monoxide, free oxygen, and even of ammonia, according to their 

 nature and the greater or less intensity of their action. The hyponitrites 

 must also intervene. 



P 



