POTOMAC RIVER WATER SUPPLY RELATIVE TO TYPHOID FEVER. 273 
in the changed condition of the surface of the soil in winter and 
summer as regards vegetation. The precipitated water is caught 
by the foliage of trees, by the grass and herbage, which clothes the 
soil everywhere. The soil itself is at the same time more firmly 
bound together by the vegetation itself. In winter all this is changed. 
The absence of vegetation leaves the loose soil ready to be washed 
into streams by rain and melting snow, carrying with it the bacterial 
vegetation.” 
^‘The majority of bacteria carried into the river are, no doubt, 
harmless, but what is to prevent the infectious micro-organisms of 
typhoid and other diseases from being washed down and being 
carried into our houses with the suspended matter? The danger in 
this is not constant but only occasional. The number of bacteria 
may have no direct significance, but it is certainly an index of the 
possible danger. It is safe to assume that Potomac water free from 
suspended matter contains from 50 to 200 bacteria in 1 cc. This will, 
no doubt, be found a low average for unfiltered water when more 
statistics have been collected for other streams whose water is used 
to supply towns and larger cities.” 
No qualitative examination of the different kinds of bacteria was 
made for want of time. 
The report of the Committee of the District Medical Society on 
typhoid fever in the District of Columbia (1894) states (p. 8.): 
As the result of one year’s observation made by Theobald Smith, a relation was 
found between turbidity and the presence of bacteria. Bacteria were most abundant 
in winter, January and February having the highest average; August, September, 
and October, the months of the greatest prevalence of typhoid fever, having the 
lowest. Bacteria, most of which are harmless, were most abundant after heavy rains, 
and their presence in association with turbidity proved the then source to be from the 
washing of the surface of the soil. 
In the latest bacteriological report on Potomac water Theobald Smith adheres to 
this statement, and says that fecal bacteria and turbidity were coincident; that is, 
that rainfall carries into the Potomac whatever may happen to be on the surface of 
the soil — clay, manure from the fields, inorganic or organic matter of any sort. The 
nature of the country through which the Potomac flows, much of it being mountainous, 
as well as the absence of large cities on its banks, diminish the risks of infection from 
this source. As the country comes more and more under cultivation turbidity and 
impurity from the washing of plowed and manure-covered land will be more common. 
The possibility of the introduction into the water of the micro-organism of typhoid 
fever is dependent upon its presence in localities washed by the Potomac and its 
tributaries. 
29643—07 18 
