BACTERIOLOGICAL ANALYSIS OF AIR. 645 



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 



FIG. 99. 



Bent funnel for use with aerobioscope. 



the soil in sterilized water and then making plates 

 immediately from the water. 



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

 organisms 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, every- 



