24 
cases and 92 colored cases, a ratio of 1 colored to 2.4 white cases, 
while in the four months of Jnly, August, September, and October, 
1906, there were reported 53 T white and 238 colored cases, a ratio of 
1 colored to 2.2 white cases. In 1905 the ratio of colored to white 
cases for the first of the above periods was 1 to 2.9, and for the second 
IDeriod (July, August, September, and October), 1 to 2.5. 
Considering these facts, it is evident that during the cool weather, 
or what may be called the off season for typhoid fever in lYashing- 
ton — that is, in January, February, March, April, May, October, 
Xovember, and December, of 1907, the factors which operate to 
cause typhoid fever in the District of Columbia fell either dispro- 
portionately heavily upon the whites or disproportionately lightly 
upon the colored. In 1907 we investigated only the cases reported 
from May 1 to Xovember 1, and as the marked disproportion in the 
cases reported among whites and colored was principally in the 
months not covered by our studies, we liaA^e no data of our own on 
which to base an explanation of this most remarkable occurrence. 
For a discussion of seasonal prevalence in relation to water borne 
typhoid see page 45. 
SANITARY CONDITION OF RESIDENCES. 
In the following table is given the general sanitary condition of 
the residences at which the patients had lived when the infection 
probably was contracted, the condition of residences of cases studied 
in 1906 being placed in the parallel column : 
Condition of residence. 
Number of 
cases. 
1907. 
1900. 
Good “ ___ 
98 
253 
Tfnirly g^nnrt « 
228 
243 
Rather bad “ _ _ . 
140 
158 
Bad “ _ __ _ - _ _ . 
57 
92 
Xot determined “__ ___ _ __ 
0 
1 
i 
523 
747 
“The definitions of these terms correspond to those used in our previous report (Bulletin 35). 
The percentage of cases among persons at residences of these four 
classes for the two periods was as follows : 
