626 APPLICATION OF METHODS OF BACTERIOLOGY 



tive of the contamination of water by sewage than is bacillus 

 coli. This opinion was under investigation by members 

 of the staff of the Massachusetts Institute of Technology, 

 who reached the conclusion that considerable reliance can 

 be placed upon the presence of this organism 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 sewage streptococcus 

 is present it is very easy to demonstrate it by microscopic 

 examination of the sediment after twenty-four to forty- 

 eight hours. In addition to this test it has also been demon- 

 strated by Winslow' 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 present 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 avail- 

 able as to the potability 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 Jour. Med. Research, 1902, vol. iii. 



