_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 mycoides_, root bacillus), which while forming ammonia 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” (_B. subtilis_), so abundantly developed in hay infusions, and one of the most abundant in cultivated soils, has together with B. ellenbachensis, B. megatherium, B. mycoides, and others, by some been credited with important action in favoring vegetation; so that a fairly pure culture of B. ellenbachensis has been brought out commercially in Germany under the name of “Alinit.” Rigorous culture experiments made by Stutzer and others have, however, failed to show any general benefit from the use of alinit in infecting either land or seeds. But there is no doubt of the _Effects of Bacterial Life on Physical Soil Conditions._—It is apparent that all conditions favoring the life of aerobic (air-needing) bacteria tend also to produce the loose, porous state (tilth) of the surface soil so conducive to the welfare of culture plants, designated by German agriculturists as “Bodengare.” Whether or not this condition is directly due to bacterial processes, as is thought by Stutzer (Landw. Presse, 1904, No. 11) it is assuredly a highly important point to be gained, and is essentially connected with the presence of humus in adequate amounts, which is also a favoring condition of abundant bacterial life. It seems that the preference given to the shallow putting-in, or even surface application of stable manure, existing in Europe, is largely based upon the marked effect upon the looseness of the surface soil, generally credited to the physical effect of the manure substance itself, but apparently largely due to the intensity of bacterial action thus brought about. [Illustration: FIG. 18.—Bacillus subtilis. (Wollny, after Brefeld.)] [Illustration: FIG. 19.—Bacteria producing ammoniacal fermentation: _A_, _C. mycoides_: _B_, _B. stutzeri_. (From Conn, Agr. Bacteriology.)] [Illustration: FIG. 20.—Bacillus megaterium. (From Migula.)]