' Quantitative Bacteriological Examination. 55 



cities. In general, any regular determination of variations 

 from a normal standard furnishes ideal conditions for the 

 bacteriological methods; and the detection by Shuttleworth 

 (Shuttleworth, 1895) of a break in a conduit under Lake 

 Ontario by a rise in the bacteria of the Toronto water- 

 supply may be cited as a classic example of its application. 



Often, however, the expert is called to pass upon the 

 character of a water of which no series of analyses is avail- 

 able and whose surroundings it may be impossible for him 

 to inspect. It has been said that single bacteriological 

 analyses of this kind are valueless; but this we believe 

 caimot always be maintained. Knowing the normal 

 bacterial range for a given class of waters, even an isolated 

 analysis may show such an excess as to have great sig- 

 nificance, as a few practical examples will make clear 

 (Winslow,-i90i). 



In- the spring of 1900 the city of Hartford, Conn., was 

 using a double supply, from the Connecticut River and 

 from a series of impounding reservoirs among the hills. 

 A single series of plates showed from 4000 to 7000 bac- 

 teria per c.c. in the water of the river, while the reservoir 

 water contained 300 to 900. The abandonment of the 

 river supply followed, and at once the excessive amount 

 of typhoid fever in the city was curtailed. 



In the fall of 1900, Newport, R. I., experienced an out- 

 break of typhoid fever, and when suspicion was thrown 

 upon the surface water-supply, chemical analysis of the 

 latter was not wholly reassuring; but there were only 334 



