PREVIOUS REPORTS UPON TYPHOID FEVER. 227 
of those below. These facts are apparent to any observer without 
chemical or biological examination. 
The amounts, kinds, and sources of pollution at the various points 
above Great Falls are reviewed in detail. The most serious sources 
of pollution in the Potomac basin are at considerable distance from 
Great Falls, but not sufficienth^ far to insure immunity from danger 
in the domestic use of raw Potomac water. 
There are two classes of pollution — sewage and industrial wastes. 
By sewage is meant the wastes occurring in the life processes of 
mankind and those resulting from domestic economy. Industrial 
wastes are those resulting from any industrial process and which, 
having no tangible value, are rejected. 
In the treatment of water containing sewage, the primar}^ object 
is to remove pathogenic organisms. By filtration, a highly polluted 
water may, within reasonable limits, be made practically as pure as 
water containing only a small amount of sewage. 
Industrial wastes offer more difficult and varied problems, on 
account of their more complex composition, difficulty of treatment, 
and varied effects. It involves detailed consideration of all the 
industries from which these wastes are derived. The effects of 
industrial wastes are various, and in nearly all cases highly detri- 
mental. Some render the water too hard for domestic or industrial 
use, some impart tastes, odors, or colors to the water. 
The author concludes that both kinds of pollution are on the 
increase, and that the sooner wise and prohibitory measures are 
taken the less trouble and expense will be incurred. 
THE POLLUTION OF THE POTOMAC RIVER AND ITS DANGERS.® 
[By Thomas N. McLaughlin, M. D.] 
In the presidential address before the Medical Society of the Dis- 
trict of Columbia, Doctor McLaughlin called attention to the impor- 
tance of this subject to the people and physicians of Washington, 
illustrating some of the chief sources of pollution by means of lantern 
slides, showing graphically the conditions described. 
Secondary to the pollution of rivers, the danger of infection by 
oysters fattened in fresh-water estuaries was particularly mentioned 
as of growing importance. 
After discussion of results obtained b}^ filtration of water supplies 
of other cities, he concludes that ^^The successful operation of an}^ 
filtration system depends upon the care, trustworthiness, and expe- 
rience of those emplo3^ed to manage the system. The degree of purit}^ 
of the filtered water is influenced by the length of time allowed for 
® Washington Medical Annals, January, 1906. 
