258 



MICROBIOLOGY OF WATER AND SEWAGE 



For practical purposes in the analysis of water, these distinctions are 

 unnecessary. 



Bad. lactis aerogenes, a short,, thick, capsulated, non-motile 

 bacterium related to B. coli, is also an intestinal organism, and must be 

 regarded as an indicator of sewage poUution. 



B. typhosus. — ^Very few instances are recorded in bacteriological 

 literature of the direct isolation of the tj^hoid bacillus from infected 

 water. The organism is not long-lived, even in pure water (eight 

 or ten days); and when exposed to the action of sewage bacteria, its 

 longevity is greatly diminished (not more than five to six days). A 

 few resistant specimens may remain alive for longer periods of time. 



Although the typhoid bacillus has been found so infrequently in 

 water, it is well understood at the present time that the purification of 

 the water supply of a town or city produces a marked decrease in the 

 number of cases and in the mortality from typhoid fever, as the following 

 table shows: (See also Fig. no.) 



Not only has such a marked improvement followed the purification 

 of public water supplies in the case of typhoid fever, but it has been 

 shown by statistics that " where one death from typhoid fever has been 

 avoided by the use of better water, a certain number of deaths, probably 

 two or three, from other causes have been avoided." 



In the routine examination of water, no' particular effort is made to 

 isolate this organism, owing to the difiSculty of the task. The tests that 

 the present-day investigator has to satisfy are extremely thorough; and 

 unless the suspected organism conforms to the whole of these necessary 

 tests it cannot be accepted as true B. typhosus. 



Msp. comma. — The spirillum, or vibrio, of Asiatic cholera is 

 an intestinal organism; and the disease it produces is spread largely 

 by water. Epidemics of cholera are more easily traced to their 



