SOIL AND SUBSOIL. 149 



earth, marl and manure, kept moist and frequently forked 

 over for better aeration. Saltpeter is similarly produced in 

 stables, corroding the mortar of brick foundations. Neverthe- 

 less, it is necessary to avoid the use, either together or at short 

 intervals apart, of Chile saltpeter and fresh manure; the ma- 

 nure if used first should be allowed to remain at least two 

 months in the soil before saltpeter is applied. 



The reduction of nitrates to nitrites and ammonia is brought about 

 by quite a number of bacteria, mostly anaerobic, and such as consume 

 combined oxygen in their development. Thus the butyric ferment, 

 which in the absence of readily reducible compounds evolves free hy- 

 drogen, will in presence of nitrates reduce the latter to nitrites, or form 

 ammonia by addition of hydrogen to nitrogen just set free by reduction. 

 Such reductive processes of course occur chiefly in soils rich in organic 

 matter, or ill-aerated. The ammonia so formed, while at first simply 

 combining with any humus acids present, may in the course of time be 

 itself reduced to the amidic condition, being thereby rendered relatively 

 inert, until again brought into action by ammonia-forming bacteria. 



Ammonia-forming Bacteria. A large number of different 

 bacteria appear to be concerned in the formation of ammonia 

 from compounds of the albuminoid group, (and probably from 

 humus). Among these is one of the most common in soils 

 (Bacillus niycoidcs, root bacillus), which while forming am- 

 monia carbonate in solutions of albumen, is also capable of 

 reducing nitrates to nitrites and ammonia in presence of a 

 nutritive solution of sugar. 



The "hay bacillus" ( H. snbtilis}, so abundantly developed 

 in ha}' infusions, and one of the most abundant in cultivated 

 soils, has together with P>. ellenbachensis. R. megatherium, B. 

 mycoides, and others, by some been credited with important 

 action in favoring vegetation; so that a fairly pure culture of 

 I*, ellenbachensis has been brought out commercially in Ger- 

 many under the name of " Alinit." Rigorous culture experi- 

 ments made by Stutxer and others have, however, failed to 

 show any general benefit from the use of alinit in infecting 

 either land or seeds. Hut there is no doubt of the 



Effects of Bacterial Life on Physical Soil Conditions. Tt is 

 apparent that all conditions favoring the life of aerobic (air- 

 needing) bacteria tend also to produce the loose, porous state 



