IS 
Service, also made a special study of the fly abimdance in these 
selected blocks. For the results of this intensive study of 32 city 
blocks in relation to bacillus carriers, see page 114. 
IMPORTED CASES. 
In determining the number of cases in wliich the infection was 
contracted out of the District of Columbia the same method was 
followed as in our study of the cases in 1907 and as published in 
Report Xo. 2, Hygienic Laboratory Bulletin Xo. 44. 
The cases fall under the following heads: 
Numl>er 
of cases. 
(а) Infection undoubtedly contracted out of the District of Columbia 103 • 
(б) Infection probably contracted out of the District of Columbia 20 
(c) Infection contracted in or out of the District of Columbia, chances about 
equal 33 
(d) Infection undoubtedly contracted in the District of Columbia 438 
(e) Infection probably contracted in the District of Columbia 71 
Total 665 
Considering the cases on the percentages of chances of the infec- 
tion having been contracted out of the District of Columbia, they 
were as follows: 
Cases. 
(а) 103 cases, chances 100 per cent 103 
(б) 20 cases, chances 75 per cent 15 
(e) 33 cases, chances 50 per cent . 17 
(d) 438 cases, chances 0 per cent 0 
(e) 71 cases, chances 12.5 per cent 9 
665 cases. Total 144 
On this estimate, about 22 per cent of the 665 cases investigated 
by us this year contracted the infection out of the District of Colum- 
bia as against about 26 per cent of the 670 cases in 1907, and about 
15 per cent of the 866 cases in 1906. 
Xo detailed epidemiological investigation was made of the cases 
which were considered as certainly or ahnost certainly having con- 
tracted the infection out of the District. Therefore, most of the 
data in this report refer to the 542 cases comprised under the heads 
c, d, and e of the above classification. 
RACE. 
Three himdred and sixty-eight, or 67.9 per cent, of the cases were 
among whites, and 174, or 32.1 per cent, among negroes. 
According to the police census for the spring of 1908 the poprda- 
tion of the District of Columbia consists of 241,920 whites and 
97,483 negroes, a total of 339,403. Thus negroes compose 28.73 per 
cent of the population, while the cases of t^'phoid fever among them 
composed 32.1 of the total number reported, showing this year 
