TYPHOID FEVER IN DISTRICT OF COLUMBIA. 
31 
The presence of typhoid bacilli in great dilution and perhaps atten- 
uation may not have the power of directly causing the disease in per- 
sons drinking such water. Water, however, containing an occasional 
typhoid bacillus may infect a community in such a way that large 
numbers of persons become bacillus-carriers. With the advent of 
the hot weather many such persons may be stricken with typhoid 
fever, just as the depressing influence of the heat is knovui to deter- 
mine the onset of diarrheal diseases and other intestinal infections. 
In other words, the presence of the typhoid bacillus in the intestinal 
tract has not always the power of causing typhoid fever. We must 
reckon with our host. The dilute and attenuated infection in the 
water may sow the seed; for the production of the disease we must 
have susceptibility, and this susceptibility may be largely brought 
about by the diminished resistance caused by the summer heat.® 
We are totally ignorant of the number of bacilli ordinarily necessar}^ 
to produce the disease. It is reasonable to assume that water con- 
taining the typhoid bacillus in great dilution may sometunes directly 
cause the disease in highly susceptible individuals. On this assump- 
tion we would expect, in a community in which the great majority of 
the population drink such water, the cases to be widely scattered and 
a very small proportion of the people to have the disease. Further, we 
must consider that the occasional and perhaps attenuated t^^phoid 
bacillus in water mav increase in danger and virulence bv contamina- 
ting milk and other beverages or foods that are favorable media for 
its rapid growth and multiplication. 
In favor of the view that the Potomac water plays an important part 
in the dissemination of typhoid fever in Washington, we have the fol- 
lowing: 
The uniform distribution of the disease throughout the city, indi- 
cating a common medium, such as water. 
The great majority (96.5 per cent) of the cases studied gave a his- 
tory of having drunk unboiled tap water within thirty days prior to 
the onset of the disease. 
The majority of the population drink unboiled tap water; and so, 
if this water contains typhoid bacilli in dilute suspension, the chances 
of infection reaching the susceptible indhdduals are favored. During 
the year 1906 one person in about every 300 of the population of the 
District of Columbia had typhoid fever and during the season of 
greatest prevalence the cases which occurred during each half- 
monthly period were widely scattered over the District. (See maps 
Nos. 1, 2, 3, 4, 5, and 6.) 
“ This same hypothesis also applies to any other means by which the infection is 
conveyed, such as direct and indirect contact. 
