260 
TYPHOID FEVER IH DISTRICT OF COLUMBIA. 
and chemical methods used in the Hygienic Laboratory and in the 
laboratory of the filtration plant are practically identical and the 
results show a general concordance. 
No satisfactory explanation has yet been given of the fact that in 
certain European cities the introduction of sand filtration of a polluted 
water supply has largely controlled the typhoid fever situation, 
whereas in America the best that sand filtration has done has been to 
reduce the death rate to an average of about 20 per 100,000, unless we 
are willing to admit that the sanitary conditions of our American 
cities are much worse than those abroad. In such a case the residual 
typhoid could be accounted for by contacts, imperfect disinfection of 
discharges, frequent infection of the milk, and an excess of those 
insanitary conditions knowm to favor the spread of a filth disease” 
such as typhoid fever. 
In our opinion, the question of by-passing Dalecarlia reservoir 
should be seriously considered from a sanitary standpoint. When the 
Avater is excessh’ely muddy sedimentation occurs slowly in Dale- 
carlia reservoir, and as the rise and fall of turbidity in the river itself 
undergoes sudden variations it not infrequently happens that the 
water at the intake is clearer than the water in Dalecarlia reservoir. 
Wlien this condition of affairs exists Dalecarlia reseiwoir is by-passed, 
thereby eliminating the Avell-known good effects of storage and sedi- 
mentation in this reservoir. This condition of affairs can be cor- 
rected by increasing the storage capacity, so that the water may be 
shut off at the intake when the river water is excessively turbid. 
We can not, however, subscribe to the opinion often expressed that 
water is necessarily of a good sanitary quality simply because it has 
been filtered through sand. 
The Washington filters have a somewhat different problem to con- 
tend with from that of the filters at Hamburg, Albaii}^, Lawrence, and 
other places where sand filtration has been so successful. The Potomac 
water differs from these other river waters in that (1) its bacterial 
content is comparatively low and (2) the suspended matter, consist- 
ing of clay, is comparatively high and of peculiar fineness. While 
the Potomac river water at the intake averages comparatively few 
bacteria per cubic centimeter it shows great and sudden variations. 
Furthermore, storage in the three reservoirs effects a destruction of 
about 55 to 86 per cent of the bacteria contained in the raw water, 
so that the Avater actually applied to the filters contains only about 
14 to 45 per cent of the original number of bacteria, or 250 to 600 
bacteria per cubic centimeter. SIoav sand filtration on a large scale, 
with Avater containing so fcAV organisms, is a special problem. 
It is evident that the interstices betAA-een the particles of sand are 
enormous in size compared AAuth a typhoid bacillus. There must, 
therefore, be some action in the filter other than mere mechanical 
straining. Where a ‘ Achmutz-decke ” is formed it is easy to under- 
