252 TYPHOID FEVER IX DISTRICT OF COLUMBIA. 
Table Xo. o. — Population of Potomac hasin u'Mch contrihutes direct sewage pollution — 
Continued. 
Distance 
above 
Great 
Falls, in 
miles. 
Popula- 
tion (cen- 
sus 1900). 
Estimated 
ponulation 
contribut- 
ing direct 
sewage 
pollution. 
Per cent 
of total 
direct 
pollution 
(c) More than 19 and less than 50 miles above Great Falls — 
Continued. 
Knoxville, Md 
41 
45 
47 
363 
896 
9,296 
150 
400 
500 
350 
Harper’s Ferix', W. Va 
Frederick, Md 
Other places 
Total 
2,200 
5 
(d) Less than 19 miles above Great Falls 
000 
0 
Grand total 
45,000 
100 
SUMMARY OF SANITARY SURVEY OF POTOMAC BASIN. 
1. The Potomac River at Great Falls drains an area of about 11,400 
square miles. 
2. The population of tliis area was estimated to be, in 1900, about 
500,000, or about 44 per square mile. 
3. The velocity of flow of the Potomac is extremely variable. It 
has been estimated that it takes from four to seven days for the water 
to travel from Cumberland to Great Falls, a distance of about 176 
miles. 
4. The discharo:e of the river has been found to varv between 900 
and 218,700 cubic feet a second. During April of the present year 
the estimated discharge exceeded the normal for that month by about 
30 per cent; during May the discharge dwindled to 50 per cent of the 
normal, but rose m Jime to a point about 12 per cent below the 
normal. 
5. The precipitation was below the normal dining both April and 
May, but was excessive dining June. 
6. The mean temperature was about 3° F. above normal in April 
and practically normal during May and June. 
7. T;\q)hoid fever prevailed to a greater or less degree in every part 
of the drainage basin. Xo data for an accurate determination of the 
degree or of its seasonal prevalence are obtainable; such as there are 
indicate strongly that its seasonal prevalence substantially coincides 
with that of Washington. 
8. The waters of the Potomac are directly polluted by sewage at 
numerous points. This direct pollution is contributed by not more 
than 45,000 or 9 per cent of the total population on the watershed. 
Of this pollution, about 80 per cent enters the river at points 176 
