BACTERIA IN THE AIR AND SOIL 1015 



strating the presence or absence of manure or sewage contamination, 

 has no practical value, since colon bacilli are found in the dejecta 

 of animals. 



Examination of specimens of soil for their numerical bacterial 

 contents is extremely unsatisfactory because the bacteria there 

 found can hardly ever all be cultivated together under one and the 

 same cultural environment. A large number arc anaerobic, others 

 again thrive at low temperatures, while again another class may 

 require unusually high temperatures. When such examinations are 

 made, however, specimens of the soil from the surface layer may be 

 taken in a sterile platinum spoon. When taken from the lower 

 levels, a drill, such as that devised by Fraenkel, may be used. This 

 consists of an iron rod the lower end of which is pointed. Just 

 above the point a movable collar is fitted. This collar has a slit-like 

 opening. The rod beneath the collar has a deep longitudinal groove 

 corresponding to the slit in the collar. A flange on the collar permits 

 opening and closing of the groove while the instrument is below the 

 ground. The drill is forced into the earth to the desired depth, 

 the groove is opened and earth is forced into the chamber by twist- 

 ing the rod. In the same manner the groove may be closed. The 

 soil obtained in this way is taken out of the chamber and a definite 

 quantity, say one gram, is dissolved and washed thoroughly in a 

 measured volume of sterile water or sterile salt solution. Fractions 

 of this are then mixed with the culture medium, plated, and cul- 

 tivated aerobically or anaerobically as desired. 



