POSSIBILITY OF INCREASED AREA OF FEVER. 13 
considerable extension of the territory in which the virulent form 
of the disease occurs, by migration out of the valley. 
Naturally the chances of spread will increase with the develop- 
ment of the Bitter Root Valley and the growth of shipments of 
cattle or movements of people to other regions. These considera- 
tions are sufficient to justify very energetic means for control where 
the virulent form of the disease now occurs and where, as will be 
shown in this bulletin, the practical eradication of the tick, and, 
consequently, of spotted fever, is entirely feasible. 
It has been shown by experiments conducted in the Institute of 
Infectious Diseases in Chicago that several species of ticks other 
than the form which occurs commonly in the Bitter Root Valley 
are capable of transmitting spotted fever. A very hopeful feature 
of the situation, however, is that in the valley there is but one tick 
species which attacks man. Therefore the other species are of no 
practical importance as regards spotted fever. Even among the 
species which feed upon the lower animals there are many thousands 
of specimens of Dermacentor venustus to every one of all other 
varieties. Moreover, means of control of this one species, such as 
wili be described in this bulletin, will serve greatly to lessen the 
number of the other forms. For these reasons, in formulating plans 
for practical eradication it is necessary to consider only the one 
dominant tick in the valley. 
There is one respect, however, in which the discovery that species 
other than Dermacentor venustus can transmit the disease may be 
of importance. The other forms occur over wide areas in the east- 
ern and southern portions of the United States. It is conceivable 
that if the disease were once introduced in the blood of a human 
being or otherwise, the other ticks might propagate it and transmit 
it in regions far outside of the territory in which the fever is now 
known to occur. But the danger on this score is not so great as 
might be thought. In the first place, in no localities in the United 
States are any species of ticks as numerous as is the fever species 
in the Bitter Root Valley and elsewhere in the Rocky Mountain 
region. Consequently, the occurrence of anything like an epidemic 
of the disease would be impossible. Only occasional or rare cases 
could be expected. In the second place, it can not be foretold 
whether spotted fever would find general conditions suitable for 
propagation in localities outside of the Rocky Mountain region. 
Nevertheless the degree of danger from this source, while perhaps 
slight, emphasizes the importance of eradication of the spotted-fever 
tick in the mountain region and also of the discovery of effective 
means of control for all species of ticks wherever they occur. 
