26 
The following table gives the source of water used for drinking 
during the thirty days j)rior to onset of illness by the 523 cases inves- 
tigated : 
Raw tap : 
Solely 
Principally 
Occasionaily 
Occasionally r?l 
Boiled tap : 
Solely 
Principally 
Occasionally 
Filtered tap : 
Solely 
Principally 
Occasionally 
Public wells or springs : 
Solely 
Principally 
Occasionally 
Bottled : 
Solely 
Principally 
Occasionally 
Private wells or springs in the District of Columbia : 
Solely , 
Principally 
Occasionally 
Various sources out of District of Columbia : 
Principally 
Occasionally 
25tl 
1ST 
4 
3 
13 
1 
2 
0 
36 
0 
1 
S 
12 
29 
15 
S 
157 
It is interesting to compare some of the figures in this table with 
those in a similar table for the cases studied by us in 1906. Thus, 
there is little difference in the proportion of cases among persons 
who used the raw tap water. In the 1907 period 1.3 per cent and in 
the 1906 period 1.3 per cent of the cases were among persons who had 
used water other than the raw tap as the sole source for drinking. 
In the 1907 period. 165. or 31,5 per cent, of the 523 cases investi- 
gated were in persons who. during the thirty days prior to the onset 
of the disease, had used water j^rincipally or occasionally for drink- 
ing from some source outside of the District of Colimibia as against 
69. or only 9.2 per cent, of the cases for the 1906 period. 
