METHODS OF INVESTIGATING BACTERIA. 809 



c. Soil. As yet no accurate methods of investigating investigation 

 the bacteria of the soil have been published. The of s 

 author has found that the best method is to take a 

 small known quantity of the soil and mix it with a 

 known quantity of sterilised distilled water ; the mixture 

 is thoroughly shaken up for a half to one hour ; and then 

 various quantities of the fluid are taken and employed, 

 as in the case of the examination of water, for a number 

 of plate cultivations. In the case of the soil, also, it is 

 of importance to examine the specimen as soon as 

 possible after it has been taken, because the saprophytes 

 multiply rapidly in the laboratory as the result of the 

 higher temperature. No trustworthy method has been 

 published with regard to taking specimens of the soil at 

 various depths in such a w r ay that all contamination 

 from without and from the adjacent layers of soil is 

 avoided. 



It is of extreme importance in the interest of hygienic 

 investigation that the methods of the bacteriological in- 

 vestigation of air, water, and soil should be improved. 



