10 
IOWA ACADEMY OF SCIENCE 
tunnel. The water taken directly from the well did not show any evi- 
dence of pollution. We believe that the water of the tunnel and shaft 
comes largely quite directly from the river through fissures in the rocks 
and hence is not properly filtered. 
CONCLUSION. 
We believe that the pollution of water through fissures in rocks 
occurs more frequently than is generally thought to be the case. But 
whether from that source or some other, pollution of public water sup- 
plies in Iowa is of common occurrence. With polluted water supplies, 
the question of epidemics of typhoid fever is, of course, a possibility at 
any time. There is great need for a thorough sanitary water survey 
of the state. The State Geological Survey has accomplished a most 
meritorious work in its study of underground waters. The report will 
be of great service to sanitarians, but there is now an urgent need for 
a survey, the prime purpose of which will be to determine whether or 
not a given water supply may be the source of disease. 
I desire to acknowledge my obligations for most of the data upon 
which this paper was based, to A. L. Grover, of our laboratory, who 
made the epidemiological investigation of the outbreak of typhoid fever 
at Cedar Falls,- to A. M. Alden, also of our laboratory, who made a 
similar investigation of the epidemic of typhoid fever at Fort Dodge 
and to M. F. Arey of Cedar Falls - W. H. Norton of Mt. Yernon and 
G. F. Kay of Iowa City for geological data. 
