BACTERIOLOGICAL ANALYSIS OF THE SOIL 631 



is then rolled on ice, just as is done in the preparation of 

 an ordinary Esmarch tube. 



The gelatin is most easily poured into the aerobioscope 

 by the use of a small, sterilized, cylindrical funnel (Fig. 

 113), the stem of which is bent to an angle of about 110 

 degrees with the long axis of the body. 



The larger part of the aerobioscope is divided into squares 

 to facilitate the counting of the colonies. 



By the employment of this apparatus one can filter the 

 air at any place, and can then, without fear of contamination, 

 carry the tubes to the laboratory and complete the analysis. 

 Aside from this advantage, the filter being soluble only the 

 insoluble bacteria are left imbedded in the gelatin. 



For general use this method is to be preferred to the 

 others that have been mentioned. 



BACTERIOLOGICAL STUDY OF THE SOIL. 



Bacteriological study of the soil may be made by either 

 breaking up small particles of earth in liquefied media and 

 making plates directly from this; or by what is perhaps 

 a better method, as it gets rid of insoluble particles which 

 may give rise to errors; breaking up the soil in sterilized 

 water and then making plates immediately from the water. 



It must be borne in mind that many of the ground-organ- 

 isms belong to the anaerobic group, so that in these studies 

 this point should be remembered and the methods for the 

 cultivation of such organisms practised in connection with 

 the ordinary methods. It must also be remembered that 

 the nitrifying organisms, everywhere present in the ground, 

 cannot be isolated by the ordinary methods, and will not 



