44 
the 10 c. c. samples examined. The low bacterial content of the 
filtered water in Xovember is interesting when considered in con- 
nection with the fact that the raw river water during this month 
averaged (our results) over 15,000 bacteria per cubic centimeter more 
than it did in either September or October. 
According to bacteriological standards of pure water, the water 
delivered through the filtration plant to the city of Washington dur- 
ing May, June, July, and August of 1907 was of a high degree of 
purity, and on this evidence alone it would appear justifiable to 
exclude this water as a factor in the conversance of typhoid fever 
infection. 
The filtered water this summer was of a better quality than it was 
in the summer of 1906; that is, as nearly as we can judge by our 
bacteriological results of this summer in comparison with those of our 
more limited studies in 1906. The improvement in the water being 
followed by the lower rate of prevalence of typhoid fever in the sum- 
mer of 1907 suggests cause and effect. The known factors, other than 
water, seemed, so far as the results of our epidemiological studies in- 
dicate, to have operated relatively to even a less extent during the 
summer of 1906 than in that of 1907. This suggests that the differ- 
ence in morbidity rate of typhoid fever for the two summers was due 
to a difference in the amount of the water-borne typhoid feA^er in- 
fection. 
HowcA^er, it should be borne in mind that the preA^alence of typhoid 
feA^er in Washington and other communities has A^aried considerably 
in different years during Avhich the conditions as to Avater, etc., have, 
so far as known, remained approximately the same. 
Further, it should be stated that the improvement in the quality 
of the Potomac PiA^er water accomplished by sand filtration in 1906 
Avas not folloAved by a loAvering of the typhoid fever rate. In cities 
where infected water is knoAvn to haA^e played a conspicuous role, 
the rule has been that the filtration or improA^ement of the Avater 
supply has been followed by an immediate impress upon the height 
of the typhoid curA’e. In Paterson, A. J., however, the decline in 
the rate was not apparent until the second year following the filtra- 
tion of the public water supply. At Lawrence, Mass., the filtration 
of the city water supply was followed the first year by a marked 
decrease, but it required three A^ears to produce its maximum effect. 
There has been much discussion in regard to the fact that in 1906 the 
improvement in the Potomac EiA^er Avater by filtration Avas not fol- 
loAved by an apparent loAvering of the t}q)hoid fever rate in Washing- 
ton. The A ieAV is held by some that this fact strongly indicates that 
little if any of the typhoid feA^er in Washington Avas eA’^er conveyed in 
the Potomac water. In this connection it is interesting to note that 
according to our results and those obtained in the laboratory at the 
