112 
Number of days elapsing between 
onset of primary and secondary 
cases. 
Number of sec- 
ondary cases. 
1908. 
1907. 
45 
2 
0 
46 
1 
1 
47 
1 
0 
48 
1 
1 
49 - 
1 
0 
50 
2 
0 
51 
0 
1 
52 
1 
0 
53 
0 
1 
54 
0 
1 
64 
1 
0 
70 
1 
0 
80 
1 
0 
84 
1 
0 
Not accurately determined 
Interval not determined, secondary 
cases being among physicians, 
nurses, helpers, or inmates of hos- 
pitals, who were more or less con- 
0 
6 
stantly exposed 
10 
12 
Total 
66 
70 
These figures do not support the view held by H. Conradi® that the 
infection is transmissible most often during the earliest days of the 
disease and frequently in the incubation period ; but they do empha- 
size the importance of exercising the utmost precautions to prevent 
the spread of infection from typhoid-fever patients from the onset to 
the end of illness. 
The cases attributed to direct contact with previous cases are indi- 
cated in red on Chart No. 2 and by chromes on maps Nos. 8, 9, and 
10. In some instances the location of the residence of the secondary 
case was some distance from that of the primary case, the infection 
presumably having been contracted during visits to the home of the 
primary case. 
Among the cases occurring in the 1908 period not definitely attribu- 
table to a known factor there were 15 which gave a history of asso- 
ciation with febrile cases suspected to be, but not reported as, typhoid 
fever. 
There was strongly suggestive evidence that 78 of the cases were 
due to infection indirectly conveyed by persons or flies from pre- 
viously existing known cases. 
In determining that conveyance of infection by flies was probable, 
the proximity of the house occupied by the primary case to that occu- 
^^Deut. med. Woch., Oct. 10, 1907. 
