13 
Our method of conducting the investigation of the cases has been 
the same for each of the three years in which we have studied typhoid 
fever in the District of Columbia. All residences within the District 
from which cases were reported were visited and inspected. For the 
data the patients themselves were questioned when their condition 
permitted it. If their condition did not permit it the statements 
of other members of the family or household were taken. 
Frequently several visits to a home were necessary before all the 
information desired could be obtained for a given case. By exer- 
cising care and patience it was endeavored to eliminate as much 
error as possible from the figures. Having followed the same plan 
of study for each of the three years we believe that differences in our 
findings for any two of the years are due to change of conditions and 
scarcely, if in any wise, to change of methods of study. 
In each of the three years the epidemiological investigation of the 
individual cases has been conducted by one of us (Lumsden), so that 
differenqes in the results from personal equation have been eliminated. 
INTENSIVE STUDY OF SPECIAL DISTRICTS. 
In addition to the above epidemiological investigations there was 
made in 1908 an intensive study of the typhoid fever situation in 32 
blocks of the city. This part of the work was done under our direc- 
tion by Passed Assistant Surgeon Norman Roberts. The study con- 
sisted in a house to house canvass of the blocks. Effort was made to 
obtain full histories of all cases of illness in these sections and to 
determine if any of the cases were typhoid fever. 
In the course of this work over 1,000 specimens of feces were 
obtained from 993 persons and examined at the Hygienic Laboratory 
for the presence of the typhoid bacillus. The specimens were obtained 
from suspected cases of illness and from healthy persons, particularly 
women and children, with a view of determining what proportion of 
the population harbors typhoid bacilli without having symptoms of 
the disease. 
In the course of this special investigation Doctor Roberts also 
collected data in regard to sanitary conditions, water and milk sup- 
plies, etc., of the households in those sections. 
The results of this special study are presented in the following 
table : 
