40 BACTERIOLOGICAL EXAMINATION OF WATER. 



establish the absence of B. typhosus becomes a very important 

 question. In view of the above considerations the work of the 

 Lawrence city filter is of interest. During the year 1899, 180 

 samples of the river water at the intake of the filter were 

 examined, and B. coli were found in all of them, the number 

 per cubic centimetre averaging 47 for the entire year. During 

 the same period 189 samples of the filtered water collected at 

 the pumping-station were also examined for B. coli, and it was 

 found in 1 c.c. of 45 of these samples. Twenty-seven of the 

 samples in which it was found, however, were collected during 

 the months of January and February. " Probably never more 

 than one colony per c.c. was present in any of these samples of 

 effluent from the city filter." It is evident from the above 

 results that seasonal variations of temperature affect the work of 

 sand filters in eliminating B. coli communis, the poorer work 

 being done during the colder months of the year. The experi- 

 ments of the State Board of Health are not yet completed ; 

 their additional studies gave somewhat contradictory results, so 

 the very important questions as to whether B. coli must be 

 completely absent from, or whether it may be allowed in, a cer- 

 tain volume of the filtered water in order to make sure of 

 the absence of the B. typhosus, must be considered still 

 unsettled. 



