EXPERIMENT STATION BULLETINS. 



465 



One ma}^ object, that llie soil as .snch has a jjroat influence upon the 

 growth of microorganisms. That is bejoud doubt. But it must be ad- 

 mitted that in order to determine the influence of phenol upon bacteria, 

 we do not figure our data i)er gram of i)henol, but per 100 cc. of nutrient 

 solution. On the contrary, the inlroduclion of the soil into the basis 

 of comparison makes the data obscure. This is easily demonstrated in 

 the case where tlie soil does not afl'ect the bacterial development. If a 

 stone weighing 100 g. is added to 100 cc. of a pure culture of B. 

 mj/coicl-cs. and 2 stones of 100 g. each to another 100 cc. of a pure 

 culture of B. mycoidcs, it is evident Ihat the development is practically 

 the same in both cases, but the computation per "100 g. of dry soil" 

 shows the first culture to give twice as high data as the second. An 

 example of the perplexities encountered in figuring on the soil as a 

 basis has been given already in the influence of acid phosphate upon 

 the sand cultures. 



Stevens and Withers* have considered the possibilities of using the 

 soil solution as the basis of all comparison, and have computed their 

 data accordingly. But they did not continue in their policy. "This 

 method of comparison probably tends to exaggerate the value of the 

 changes occurring, and from a practical viewpoint a comparison by 

 the third method is probably the most serviceable since it pictures ap- 

 proximately the relative nitrifying power of two cultures of equal 

 weight." It is the author's belief that the "practical viewpoint" of 

 Stevens and Withers prevented them from obtaining the data and con- 

 clusions presented in this paper. 



For this reason, all further discussion of experiments is based on 

 equal amounts of liquid medium. All data of Table I have been com- 

 puted in mg. NH3 per 100 cc. of soil solution. Table VI shows data 

 which will lead to conclusions essentially different from, and even con- 

 trary to those of the former paragraphs. 



TABLE VI. 



Milligrams NH3 formed by Bacillus mycoides in 100 cc. Soil Solution. 



Series I. 



*Centralblatt f. Bakt. II Abteilung, Bd. 23, p. 372. 

 59 



