148 PATHOGENIC BACTERIA. 



amount of this soil is mixed thoroughly and the mixture 

 solidified upon the walls of an Bsmarch tube. The col- 

 onies are counted with the aid of a lens. Fliigge found 

 in virgin earth about 100,000 colonies in a cubic centi- 

 meter. 



Samples of earth, like samples of water, should be 

 examined as soon as possible after being secured, for, 

 as Giinther points out, the number of bacteria changes 

 because of the unusual environment, exposure to increased 

 amounts of oxygen, etc. 



The most important bacteria of the soil are those of 

 tetanus and malignant edema, in addition to which, how- 

 ever, there are a great variety which are pathogenic for 

 rabbits, guinea-pigs, and mice. 



