SOIL MICROBIOLOGICAL EQUILIBRIUM 751 



stimulating effect when added to the soil some time before the crop is 

 planted. This was attributed 49 to a changed bacterial population. A 

 bacterial flora of 9| millions per gram, as determined by the plate 

 method, was depressed by the addition of the disinfectant (fig. 66); 

 it soon increased rapidly, reaching, within a month after the evaporation 

 of the disinfectant, 50 millions; the numbers then slowly fell but re- 

 mained above the original number. The normal flora of the soil 

 consisted of 75 per cent non-liquefying bacteria, 20 per cent actinomyces 

 and 5 per cent gelatin liquefying forms. As a result of treatment with 

 carbon bisulfide, the non-liquefying organisms were greatly increased, 

 while the actinomyces were reduced and did not return to the original 

 proportion for at least two years. The denitrifying bacteria were 

 completely destroyed, while the pectin-fermenting organisms were 

 reduced. As a result of these studies, Hiltner and Stormer came to 

 the following conclusions: 



1. By destroying the existing bacterial equilibrium in the soil, carbon bisul- 

 fide opens the way for an entirely new bacterial development. This is achieved 

 through the unequal retardation in the growth of the different groups of bac- 

 teria. Hence certain groups become disproportionately prominent, while others 

 are almost entirely suppressed. 



2. The rapid increase in the numbers of the bacteria is followed by a more in- 

 tense transformation of plant food substances. Decomposition and fixation 

 processes result in an accumulation of readily available nitrogen compounds 

 utilized by the crops. Hence the action of carbon bisulfide is in the nature of 

 nitrogen action. 



3. The initial suppression of the nitrifying species becomes of advantage in 

 that the nitrogen compounds, simplified by other species, are prevented from 

 being rapidly changed into nitrates and being leached out of the soil. 



4. The more or less permanent suppression of the denitrifying organisms must 

 be regarded as an additional factor favoring plant growth. 60 



Van Suchtelen 51 found that CS 2 stimulates the decomposition of 

 organic matter, as indicated by the C0 2 production; 12 kgm. of soil 



49 Hiltner and Stormer, 1903 (p. 12); Hiltner, L. Uber neuere Ergebnisse 

 und Probleme auf dem Gebiete der landwirtschaftlichen Bakteriologie. Jahresb. 

 Angew. Bot., 5: 200-222. 1907; Centrbl. Bakt. II, 38: 228. 1912; Stormer, 1907 

 (p. 750). 



60 The observations of Hiltner and Stormer were confirmed by Moritz, J., 

 and Scherpe, R. Uber die Bodenbehandlung mit Schwefelkohlenstoffe und 

 ihre Einwirkung auf das Pflanzenwachstum. Arb. K. Gesundhsamt. Biol. 

 Abt., 4: 123-156. 1904; also Arb. K. Biol. Anst. Land. Forstw., 7: 353-425. 

 1909; Centrbl. Bakt. II, 13: 573. 



61 Van Suchtelen, 1910 (p. 720). 



