60& ELEMENTS OF WATER BACTERIOLOGY 



The results presented in the diagram on page 6oa 

 offer an interesting example of the value of the total 

 count of bacteria as compared with the estimation 

 of B. coH. This chart, prepared by Mr. J. W. Acker- 

 man, the Engineer of the Auburn, N. Y., Water Board^ 

 shows by the vertical lines the total count and by the 

 crosses the presence of colon bacilli in the water supply 

 of Auburn drawn from Lake Owasco. In the year 

 illustrated in this diagram, and in other years, before 

 and after, the total count of bacteria rose sharply at 

 the time of the spring thaw, while colon bacilU were 

 on the whole more abundant during the summer. 

 The explanation of this phenomenon probably is that 

 a certain proportion of colon bacilli are always contrib- 

 uted by the small brooks which enter the reservoir 

 from agricultural land which, not being of human 

 origin, have but little significance. At the time of 

 the spring thaws, which for the most part wash an 

 open farming country, the normal contribution of B. 

 coh from the fields is obscured by the rain and melting 

 snow, while only the rise in total count registers the 

 fact that contaminating material of all sorts is being 

 washed into the lake. With this contaminating material, 

 for the most part of a harmless nature, human excreta 

 are washed in from certain points on the watershed, 

 and in the spring of 1908 these excreta contained 

 specific typhoid infection and an epidemic in Auburn, 

 was the result. 



In this case then the total count of bacteria was a 

 more accurate index of danger than the colon content. 



