570 BACTERIA IN THE SOIL. 



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 the soil. Thus Prankland 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 m the soil at a 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 the earth 

 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 at a 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-one days. These results indicate 

 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 microorganisms. 



