BACTERIA IN THE SOIL. 645 
The results obtained in the researches referred to, in which nutri- 
ent gelatin was used as a culture medium, are no doubt very in- 
complete, not only on account of the liquefaction of the gelatin by 
common liquefying bacilli before other species present have formed 
visible colonies, but also because this is not a favorable culture me- 
dium for some of the species present in thesoil. Thus Frankland has 
succeeded in isolating a nitrifying ferment which he calls ‘‘ Bacillo- 
coccus,” which grows abundantly in bouillon, but fails to grow in 
nutrient gelatin. Winogradski has also obtained in pure cultures a 
nitrifying ferment from the soil in the vicinity of Zurich, which he 
has called ‘‘ Nitromonas.” 
Comparatively few micrococci are found in the soil, while in the 
air they are usually found to be more abundant than bacilli. This 
is perhaps due to the fact that the bacilli are more promptly destroyed 
by desiccation and the action of sunlight. 
Several bacteriologists have made investigations relating to the 
duration of vitality of pathogenic bacteria in the soil. Frankel found 
that in Berlin the bacillus of anthrax, in Esmarch roll tubes, when 
buried in the soil ata depth of two metres, only occasionally gave 
evidence of growth, and at three metres no development occurred. 
The comparatively low temperature at this depth was no doubt an 
important factor in influencing the result. The cholera spirillum in 
the months of August, September, and October grew at a depth of 
three metres, but in the remaining months of the year failed to grow 
at two, while growth occurred at one and one-half metres. The 
bacillus of typhoid fever grew at three metres during the greater 
portion of the year. 
Giaxa has made extended and interesting experiments with the 
cholera spirillum, cultures of which he added to different kinds of 
soil (garden earth, clay, sand) and placed at different depths below 
the surface—one-quarter, one-half, and one metre. Some of theearth 
was sterilized and some was not. In the unsterilized earth he found 
the cholera spirillum in considerable numbers at the end of twenty- 
four hours at the greatest depth tested (one metre), but at the end of 
forty eight hours it had disappeared in five experiments out of seven 
—the lowest temperature at this depth was 20° C. In the sterilized 
soil the result was different ; the cholera spirillum was present in 
enormous numbers at the end of four days ata depth of a metre, 
and was still found in smaller numbers at the end of twelve days, but 
had disappeared at the end of twenty-onedays. These resultsindicate 
that the presence of common saprophytes in the soil is prejudicial to 
the development of the cholera spirillum, and that under ordinary 
circumstances it succumbs in the struggle for existence with these 
more hardy microérganisms. 
