THE SIGNIFICANCE OF B. COLI IN WATER. 87 



broth. The results of these comparative tests may be 

 tabulated as follows: 



PERCENTAGE OF SAMPLES OF WATER CONTAINING B. COLI. 



LAWRENCE EXPERIMENT STATION (MASSACHUSETTS STATE BOARD O F 

 HEALTH, IQOl). 



Effluent of Outlet of Tap, Tap, Experiment 



Filter. Reservoir. City Hall. Station. 



In I c.c 18.14 8.57 4.07 1.87 



Iniooc.c 38.12 23.30 15.54 15.54 



It appeared that the use of the larger volume of water 

 gave very little additional information, and indeed the 

 real difference between the waters examined is rather 

 obscured by the use of the large samples. 



In 1900 Clark and Gage (Clark and Gage, 1900) re- 

 ported some specially instructive observations made when 

 certain of the underdrains of the Lawrence municipal 

 water- filter were relaid in the autumn of 1898. In doing 

 this work the sand on some of the beds was seriously 

 disturbed; and in December, after the work was com- 

 pleted, B. coli was found in i c.c. of the filtered efflu- 

 ent in 72 per cent of the samples examined. In Janu- 

 ary and February the organisms were found in 54 per 

 cent and 62 per cent of the samples, respectively, while 

 in March the number fell to a normal value of 8 per cent. 

 Corresponding to this excess of B. coli in the city water, 

 there were 12 cases of typhoid fever in December, 59 cases 

 in January, 12 in February, and 9 in March, all during 

 the early part of the month. The authors conclude that 

 " when filtering a river- water as polluted as that of the 



