8 
ETIOLOGY. 
1. GEOGRAPHIC DISTRIBUTION. 
Montana . — The disease has been known in the valley of the Bitter 
Boot River in western Montana for about twenty years. It is sharp]}" 
localized on the west bank of the Bitter Root River, no cases having 
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 3 "ear 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 
Avill be seen in the appendix. 
Idaho . — The disease has also been known clinically in Idaho for 
many }"ears, the lirst published description having ])een made by Dr. 
E. E. Maxey, in the Portland iNIedical Sentinel for October, 1899 (1). 
An unpublished symposium on the disease by i^arious Idaho pli 3 "si- 
cians was made by Maj. M. "W. AVood, U. S. Army, 1898, to the Sur- 
geon-General of the Army. In Idaho the disease prevails throughout 
almost the entire i^alley of the Snake Rii"er, its tributaries* and the 
foothills of the neighboring mountains. 
Mevada . — I am informed by Maj. AA^. R. Kendall, U. S. Army, that 
the disease also prevails in the i^alley of the Quinn River in northern 
Nevada. 
Wyoming . — Cases hai"e been reported this spring at Cody and 
Meeteetse. 
Oregon . — The mild form of the disease has been reported in eastern 
Oregon. 
2. CLIMATE. 
The disease does not prev^ail south of or north of 17°. It pre- 
vails at an ai^erage elei^ation of about 3,o00 to 1,00<) feet aboAT sea 
leA^el. 
o. SEASON. 
The disease preA^ails exclusiA^ely in the spring and early summer. 
In the Bitter Root cases the earliest was March IT and the latest JuIa" 
20 . 
I. 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. 
