334 APPLIED BACTERIOLOGY 



investigated the nature of the soil in graveyards, and he 

 finds, on the whole, that the bodies do not greatly influence 

 the number of micro-organisms found. According to 

 Kirchner, the freedom of the ground water from bacteria is 

 due to the great porosity of the soil, which acts as a very 

 efficient filtering medium. 



Examination of Soil. — When the deeper layers are to be 

 examined, care must be taken to prevent contamination 

 with the other portions, particularly the upper layers. 

 Frankel has devised an ingenious instrument for taking 

 samples of earth from various depths. This takes the form 

 of a borer, which contains at its lower end a small cavity, 

 which can be closed up by turning a handle, or opened by 

 turning in the opposite direction. The borer is pushed 

 down to the necessary depth ; the handle is then turned, 

 with the result that the earth enters the cavity ; the handle 

 is again turned, enclosing the sample of earth completely ; 

 the borer is then withdrawn. The soil can now be examined 

 by thoroughly mixing a very small quantity of the earth 

 with melted nutrient gelatine, which can then be poured on 

 a plate, or better, made into a roll culture by Esmarch's 

 method. Another method is to wash the soil with sterile 

 water, which is examined as usual by the plate method. 



