8 
ETIOLOGY. 
1. GEOGRAPHIC DISTRIBUTION. 
Montana . — The disease has been known in the vallev of the Bitter 
Hoot River in western Montana for about twenty years. It is sharply 
localized on the west hank of the Bitter Root River, no cases havino- 
been known to occur in persons on the east side of the river who had 
not a short time previously visited the west side. The infected local- 
ity extends from Loo Loo to Como, a distance of about 50 miles. Cer- 
tain places in the valley seem to be more heavily infected than others. 
Nine cases have also occurred in the canyon of Rock Creek, about 10 
miles south of Bonito and 20 miles east of the Bitter Root. 
This year information was obtained from Dr. L. A. Gates, of Bridger, 
Mont., about 100 miles east of the Bitter Root, of the prevalence of 
the disease in that locality. A report of two cases described by him 
will be seen in the appendix. 
Idaho . — The disease has also been known clinically in Idaho for 
many y^ears, the tirst published description having- been made by Dr. 
E. E. Maxev, in the Portland ^Medical Sentinel for October, 1899 (1). 
An unpublished symposium on the disease hi' various Idaho physi- 
cians was made by Maj. M. M. Mood, L. S. Army, 1898, to the Sur- 
geon-General of the Army. In Idaho the disease prevails throughout 
almost the entire valley of the Snake River, its tributaries, and the 
foothills of the neighboring mountains. 
Mevada . — I am informed by Maj. W. R. Kendall, U. S. Army, that 
the disease also prevails in the valley of the Quinn River in northern 
Nevada. 
Wyoming . — Cases have lieen reported this spring at Cody and 
Meeteetse. 
Oregon . — The mild form of the disease has lieen reported in eastern 
Oregon. 
2. CLIMATE. 
The disease does not prevail south of l(h or north of 47°. It pre- 
vails at an average elevation of about 3.U00 to 4,00<) feet above sea 
level. 
o. SEASON. 
The disease prevails exclusively in the spring and early summer. 
In the Bitter Root cases the earliest was March IT and the latest July 
20 . 
4. OCCUPATION. 
All occupations that cause the person to be exposed to the bite of 
ticks, such as stockmen, and especially sheep herders, miners, pros- 
pectors, lumbermen, ranchmen, and those whose duties take them into 
the brush, are subject to the disease. 
