ACKNOWLEDGMENTS. 
In compliance with the instructions of the Surgeon-General this 
investigation into the causes of typhoid fever in the District of Colum- 
bia was carried out in cooperation with the health department of the 
District. We especially desire to express our appreciation of the 
valuable assistance and hearty cooperation of Dr. William C. Wood- 
ward, the health officer of the District, and his assistants. From the 
official records Doctor Woodward gave us numerous transcripts and 
caused special compilations to be made. He further acquainted us 
with important factors influencing local conditions, and in other 
ways helped us with suggestions growing out of his long experience 
with public health matters in the District. 
We desire to express our obligation to the officers and employees of 
the Washington filter plant, especialH to Captain Cosb}^, Mr. Hardy, 
and Mr. Longley for much valuable information relative to the filtra- 
tion of the Potomac water suppl}^ and for placing at our disposal the 
results of their bacteriological determinations and chemical analyses. 
We are indebted to Dr. W. A. Wliite, superintendent of the Gov- 
ernment Hospital for the Insane, for material assistance and for 
information relative to typhoid fever in that institution. 
To Mr. M. O. Leighton, chief of the hydrographic division of the 
United States Geological Survey, we are indebted for information and 
for the use of a manuscript entitled ^^The Potomac River Basin, 
Water-Supply Paper No. 192,’’ by Horatio M. Parker, and also for a 
map of the Potomac watershed, upon which our special notations 
have been made. 
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