43 
These results sIioay the great extent of bacterial purification which 
the water underwent in its passage through the storage reservoirs 
and filter beds. 
The effluent from the filter beds during the period extending from 
May 15 to August 31 can not be regarded from a bacteriological 
standpoint other than as a water of good sanitar}^ qualit}". During 
this period, of the 84 samples of which counts Avere made by us, the 
a Average number of bacteria per cubic centimeter was about 31. 
Ninety-one samples were examined in quantities of 0.1 c. c., 1 c. c., 
and 10 c. c., for the presence of the colon bacillus. In none of the 
0.1 c. c. and 1 c. c. quantities was B. coli found, and of the 10 c. c. 
quantities, B. coli was found in only 2, or about 2.2 per cent. 
In 1906 the samples of Avater, taken at interA^als of a few days 
during the period from July 25 to August 31, from the filtered water 
reserAmir, and examined by us, showed an aA^erage of 44 bacteria per 
cubic centimeter. Of 13 samples examined in this period, B. coli was 
found in 1 c. c. once and in 10 c. c. tAvice. Unfortunately the number 
of samples from the filtered Avater reservoir examined by us in 1906 
was too small to compare aptly with the results of 1907, but during 
the period extending from July 16 to August 31, 1906, Ave examined 
60 samples of tap Avater taken from taps in A^arious parts of the city. 
During this period the av^erage number of bacteria per cubic centi- 
meter in the tap Avater Avas about 67, and of the 60 samples, B. coli 
Avas found in quantities of 1 c. c. twice, and in quantities of 10 c. c. 
sixteen times, or in about 3.3 per cent of the 1 c. c. samples and in 
about 26.6 per cent of the 10 c. c. samples. 
It will be observed in the aboA^e tables that the remarkably high 
degree of purit}^ of the water accomplished by the storage and filtra- 
tion in the summer of 1907 Avas not maintained during September 
and October. According to our OAvn results, the total bacterial con- 
tent of the filtered Avater during September aA^eraged 80 per cubic 
centimeter, and during October, 84 per cubic centimeter. In Sep- 
tember, of the 1 c. c.. samples examined, B. coli was found in 4.3 per 
cent and of the 10 c. c. samples in 17.4 per cent. In October, B. coli 
was found in 3.6' per cent of the 1 c. c. samples and in 26 per 
cent of the 10 c. c. samples examined. In this connection it is in- 
teresting to note that Dalecarlia, the principal sedimentation reser- 
voir, was by-passed from August 21 to December 31, 1907. 
It should be stated that at present the generally accepted Anew is 
that the colon bacillus is only an index of pollution. It suggests 
danger, but not the amount of danger. In other Avords, a Avater may 
contain a large number of colon bacilli and yet be entirely free of 
typhoid bacilli. 
In NoATinber the aA^erage bacterial content of the filtered water was 
63 per cubic centimeter, and B. coli was found in 16 per cent of 
