IOWA ACADEMY OP SCIENCE 
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of the typhoid organisms disappear before the end of a week. It 
is, however, necessary to set the limit at complete disappearance, 
although it has been generally noticed that there are often a few 
seemingly more resistant individual germs that persist for an 
appreciably longer time than the average.” 
The low death rate from typhoid fever is well shown where fil- 
tered water is used as in the case of the city of Amsterdam, Hol- 
land, with a population of a half million, which has a death rate 
varying from 8% to 19 per 100,000. Taking the city of Lawrence, 
Mass., which has had a particularly high death rate of typhoid fever, 
we find that the death rate varied from 48 to 123 per hundred thou- 
sand. Lawrence used unfiltered water. Taking a few illustrations 
of the interior of the country, we find that the death rate of typhoid 
fever in some cases is unusually high, as in the city of Denver, 
where the number has fluctuated from 30 to 217 per hundred 
thousand population. The cities taking their supply from the 
Great Lakes are not exempt from danger; this is shown in the 
death rate from typhoid fever; in Chicago, prior to the installa- 
tion of the present drainage canal, the death rate fluctuated 
from 31 to 160 per hundred thousand. It may be of interest to 
note in this connection that the city of Des Moines has an unusually 
low death rate from typhoid fever. 
Mr. A. M. Bleile, who made a study of the sources of public water 
supplies of Ohio, makes this statement with reference to the Scioto 
River, which furnishes the city of Columbus with water: ‘There 
is not a progressive increase in the number of bacteria straight 
down stream. In other words, it is apparent that the large number 
of bacteria which gain access to the river are lost in some way, 
that is, that the water purifies itself as it is carried on through the 
stream bed. This can best be seen if we compare the figures shown 
by a station below town with the figures obtained at the station 
below, above the next town. Just how much purification takes 
place in a running stream and how this purification or destruction 
of bacteria is effected, are moot questions. Several causes are 
here invoked. It is known that exposure to sunlight will kill off 
many forms, and it is further known that aeration, while it will at 
first increase the number of bacteria, will eventually cause the 
destruction of a large number of them. Then, sedimentation may be 
a factor of some moment, though that this should be very great 
in the rivers here in consideration, does not seem probable. Then 
it is to be borne in mind that our bacteria must be of a low specific 
gravity, not much different from that of water, and that they there- 
