February, ’20] PARKER: DERMACENTOR VENUSTUS BANKS 
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pose that a certain rodent is the medium through which the disease 
becomes endemic. Then, since the distribution of most rodents and 
their relative abundance is largely dependent upon the distribution of 
certain types of vegetation favorable to them, the value of the eradi¬ 
cation of ticks and even of the particular rodent involved, is limited by 
the very probable facts that a certain degree of tick reinfestation is 
very possible and that since the natural habitat of the rodent remains, 
reinfestation by this rodent would also take place, with the possibility, 
at least, of a recurrence of the disease. On the other hand, if this 
rodent were known, or it might be that more than one species would 
be involved, steps could perhaps be taken to prevent its reappearance. 
In the case of certain rodents, such a course would be entirely possible 
and the probability of future tick reinfestation would be of negative 
importance. 
At the present time, the methods of tick control employed are rodent 
destruction (directed particularly against the Columbian ground 
squirrel); the restriction of grazing; dipping and hand picking of 
stock; quarantine and cultivation. Under these measures, the mini¬ 
mum time to expect apparent results is three seasons, and complete 
eradication will take from five years on, depending upon the degree 
of cooperation obtained from the residents and the thoroughness 
with which the state can carry out its end of the control program. 
Hence, the chance that there may be some simpler means of 
solving the problem than those now in use is not only an invit¬ 
ing field for research, but also a very pertinent question at the 
present time, when there is the probability that it will be necessary 
to extend the work over a greatly increased area. This possibility 
immediately directs attention to the fact that methods of tick con¬ 
trol depend upon local conditions, so that to secure the best results, 
variations in method, from place to place, are quite essential. The 
conditions which make such variations necessary are: differences in 
the hosts of the larval and nymphal ticks, differences in the hosts of 
adult ticks, differences in economic conditions, differences in the char¬ 
acter of the vegetation and soil covering which predetermine the species 
and the relative abundance of the rodent hosts of the immature ticks, 
and finally differences in the habits of ticks, which often show con¬ 
siderable variation with short distances. Space does not permit that 
these factors be discussed, nor is it necessary, except to point out that 
a further expansion of the work would mean the working out of a sys¬ 
tem of control varied here and there, to adapt it to local conditions. 
This is a difficult thing to do, especially in a farming community. As 
an alternative is the possibility of finding a simpler way of checking 
the fever, that is, one of more general application. The latter step 
