640 BACTERIOLOGY. 



positively indicative of the contamination of water 

 by sewage than is bacillus coli. This opinion has 

 recently been under investigation by members of the 

 staff of the Massachusetts Institute of Technology, and 

 they have reached the conclusion that considerable 

 reliance can be placed upon the presence of this organ- 

 ism as an indication of sewage pollution of water. 



The presence of the sewage streptococcus is most 

 readily shown in the sediment in fermentation tubes 

 inoculated with water under examination. If the sew- 

 age streptococcus is present it is very easy to demon- 

 strate it by microscopic examination of the sediment after 

 twenty-four to forty-eight hours. In addition to this 

 test it has also been demonstrated by Winslow l that the 

 estimation of the degree of acidity of the contents of the 

 fermentation tube is a safe indication of the presence of 

 the sewage streptococcus. When this organism is pres- 

 ent the acidity rises far more rapidly and to a greater 

 height than is the case when it is absent, so that in this 

 way an additional indicator is available as to the pota- 

 bility of a water under examination. 



BACTERIOLOGICAL ANALYSIS OF AIR. 



Quite a number of methods for the .bacteriological 

 study of the air exist. In the main they consist either 

 in allowing air to pass over solid nutrient media (Koch, 

 Hesse) and observing the colonies which develop upon 

 the media, or in filtering the bacteria from the air by 

 means of porous and liquid substances, and studying the 

 organisms thus obtained. (Miguel, Petri, Strauss, Wiirz, 

 Sedgwick-Tucker.) Because of their greater exactness, 

 the latter have supplanted the former methods. 



1 Winslow : Jour. Mecl. Research, vol. iii., 1902. 



