696 BACTERIOLOGY OF THE SOIL, WATER AND AIR 
Isolation and Culture.— The organisms of the Siibtilis-Mesentericus 
Group grow with great hixuriance upon ordinary cultural media. The 
colonies on agar are irregular in shape, opaque, and spread rapidly. 
Gelatin colonies are similar in appearance and the medium is rapidly 
liquefied. Blood serum and casein are also liquefied. Milk is coagu- 
lated and the coagulum dissolves; the reaction, at first slightly acid, 
soon becomes alkaline as a rule. Indol, ammonia in considerable 
amounts, 1 hydrogen sulphide and other products of protein decom- 
position are formed in glucose-free media and cultures of the organ- 
isms contain very powerful soluble proteases. The addition of glucose 
to such media definitely prevents the formation of such proteases, 
however." 
As a rule the Subtilis-Mesentericus bacilli are non-pathogenic, but 
Siberschmidt^ and others have described a type of ophthalmia in 
Switzerland, apparently incited by B. subtilis, and Spiegelberg,^ 
Fliigge,^ x^rdoin*^ and more recently Vincent^ have presented evidence 
in favor of the view that the organisms may become temporarily 
localized in the intestinal tract and incite severe gastro-intestinal 
disturbances. 
It is stated that B. subtilis difters from B. mesentericus and other 
members of the group in its inability to ferment glucose. The other 
varieties form acid but no gas from this sugar. 
The foregoing obser^'ations have shown that the normal bacterial 
flora of the soil plays a prominent part in agriculture; it transforms 
dead unavailable organic matter and certain minerals as well into 
compoimds suitable for plant food. It is essential to relate in some 
detail the manner in which these transformations are accomplished. 
The amount of nitrogen available at the present time for synthesis 
by plants exists chiefly in an organized state, and as nitrates in the 
soil. Nitrates are very soluble and it is obvious that large amounts 
of available nitrogen are yearly carried in solution to the ocean where 
they are practically lost. Brandt^ estimates this loss to be about 
40,000,000 kilograms annually. It is obvious that this loss must be 
compensated for. 
It is a matter of common observation that soil left uncultivated 
gains in fertility from year to year and in 1875 Berthelot, and Xobbe 
and Hiltner^ made the important discovery that nitrogen from the 
air is fixed in the soil. It was found that soil heated to 100° C. lost 
its power of fixation of nitrogen, suggesting that microorganisms 
played a part in the process. In 1888 Beijerinck^" made the very 
important discovery that nodules^^ upon the roots of leguminous 
' Kendall, Day and Walker: Loc. cit. '^ Kendall and Walker: Loc. cit. 
3 Ann. Inst. Pasteur, 1903, 17, 268. ■• Jahrb. f. Kinderheilk., 1S99, 49, 194. 
5 Ztschr. f. Hyg., 1894, 17, 272. « Th^se de Paris, 1898, p. 78. 
' Intestinal Toxemia in Infants, 1911. 
* Report Kommission zur Untersuch. d. deutsch. Meere, 1899-1901. 
' Landwirtsch. Versuchsstat., vol. 45. '" Bot. Zeitung, 1888, p. 725. 
" These nodules were first described by Hellriegel (Tageblatt Naturforsch. Vers., Berl., 
1886, p. 290) and Willforth (Ibid., 1887, p. 362). 
