244 ESSENTIALS OF BACTERIOLOGY 



When the deeper layers are to be examined, some precau- 

 tions must be taken to avoid contamination with the other 

 portions of the soil. One method, very laborious and not 

 often practical, is to dig a hole near the spot to be examined 

 and take the earth from the sides of this excavation. 



FrankePs Borer. Frankel has devised a small apparatus 

 in the form of a borer, which contains near its lower end a 

 small cavity, which can be closed up by turning the handle, 

 or opened by turning in the opposite direction. 



It is introduced with the cavity closed, and when it is at 

 the desired depth, the handle is turned, the earth enters the 

 cavity, the handle again turned, incloses it completely, and 

 the borer is then withdrawn. 



The earth can then be mixed with the culture-medium in a 

 tube, and this gelatin then rolled on the walls of the tube after 

 the manner of Esmarch, or it can be poured upon a plate, 

 and the colonies developed therein. 



Another method is to wash the earth with sterilized water, 

 and the water then mixed with the culture-medium, as many 

 of the germs are taken up by the water. 



The roll-cultures of Esmarch give the best results, many of 

 the varieties usually found being anaerobic. 



Animals inoculated with the soil around Berlin are said to 

 die almost always of malignant edema, and the soil of other 

 towns produces tetanus. Many of the germs found are nitro- 

 gen formers and play a great role in the economy of the soil. 



Bacteria and Soil Fertility. Nitrifying organisms are 

 found in the superficial layers of the earth. Organic matters 

 found in sewage and in the fecal evacuations of animals form 

 the basis for their activity, whereby nitrates, ammonias, and 

 nitric acid result. The nitrogen necessary for the growing 

 plant is thus produced. The nitromonas of Winogradsky 

 belongs to this group. The soil tends to destroy ordinary 

 disease-bacteria in a short time, but spores may remain dor- 

 mant for a number of years, as, for instance, the spores of 

 anthrax. 



As bacteria are instrumental in transforming organic 



