35 
For the same 88 cases the lowest difference between the monthly 
average maximum and minimum temperature for Missoula was 19.6° F. 
(2 cases), the highest 35.8° F. (2 cases); for 2 cases there was a monthly 
average difference of 19.6° F ; for 70 cases there was a monthly average 
difference from 21.7 to 29.8° F., inclusive; for 16 cases there was a 
monthly average difference from 30.4 to 35.8° F. 
Thus a monthly average maximum of 63 to 73° F., inclusive, obtained 
in 59 out of 88 cases, or 67 per cent of the cases; a monthly average 
minimum of 37 to 46° F., inclusive, obtained in 58 out of 88 cases, or 
65.8 per cent of the cases; of 88 cases 70 cases, or 79.5 per cent, 
occurred during an average monthly difference of 21.2 to 29.8° F. 
between maximum and minimum temperature, and 55 of these cases, 
or 60.2 per cent of the 88 cases, occurred during a monthly average 
difference of 25.2 to 29.7° F., inclusive, between the monthly maximum 
and monthly minimum. 
It would therefore appear that, so far as can be concluded from the 
data at our disposal, there seems to be some connection, either direct 
or indirect, between the temperature of the air and the development 
of cases, in that up to a certain point an increase in temperature is 
coincident with the development of cases, while beyond that point a 
further increase in temperature seems not to favor the appearance of 
new cases. Of course an increase in temperature increases the amount 
of water resulting from the melting snow, but there finally comes a 
time when the supply of snow is greatly decreased, hence a further 
increase in temperature would not have the same effects upon the 
amount of water in the valley. 
Our data upon these points are not sufiSciently exact to permit of 
positive conclusions, but such as the data are they tend to support 
rather than to negative the popular idea that the melting snow has 
some direct or indirect connection with the development of cases, or 
at least they tend to show that conditions which favor the melting of 
the snow also favor the appearance of cases of spotted fever. 
Taking the amount of precipitation, including rain, hail, sleet, and 
mhlted snow (not from the mountains), we find that 14 cases occurred 
in six months showing a total monthly precipitation of 0.37 to 0.68; 
50 cases occurred in eleven months showing a total monthly precipita- 
tion from 1.02 to 1.98; 3 cases occurred in one month showing a pre- 
cipitation of 2.78; 7 in a month showing precipitation of 3.84, and 14 
in 2 months showing precipitation of 4.19 and 4.53. 
The lowest precipitation in any month during which a case developed 
was 0.37 (1 case); the highest number of cases in reference to precipi- 
tation were as follows: 6 cases, 0.65; 9 cases, 1.2; 9 cases, 1.44; 15 
cases, 1.28; 7 cases, 3.84; 6 cases, 4.19; 8 cases, 4.53. 
From this it is seen that in general fewer cases have developed 
during the epidemic months with a precipitation under 1 than with 
