EKADICATION OF THE KOCKY MOUNTAIN SPOTTED FEVER TICK. 9 
gouging. The last female on sheep No. 10 would probably have 
become engorged had it been fertilized, for fertilized females engorge 
rapidly, whereas with infertile females engorgement is slow. 
THE APPLICATION OF THE INFORMATION OBTAINED TO PRACTICAL 
ERADICATION. 
The main point to be considered in the last experiment is the fact 
that of 33 females put on sheep No. 10, only 1 fed sufficiently to lay 
eggs. There were in all, however, 6 females which stood a fair 
chance of engorging, so that it is difficult to say what percentage of 
females that get on a sheep in nature will engorge to repletion. If 
we assume that 6 females would have fed to repletion in nature, we 
find that 5.5 per cent of those females which got on the sheep became 
engorged. In the experiment with 2 sheep, at the end of 6 days these 
animals had picked up at least 19 females, of which 13 females at- 
tached. At the same rate in 30 days sheep No. 10 would have had at- 
tached 80 females and would have picked up 94 females. If we take 
5.5 per cent of 94 we have 5.17 females which would engorge to reple- 
tion in a month. We would have to assume this many to be the maxi- 
mum for the sheep with heavy wool in the experiment. The mini- 
mum would be 0, since there were 2 sheep which had no females at- 
tached at the examination. It would be impossible to strike an aver- 
age, but let us assume that each sheep would breed, on an average, 2 
ticks per month. We would then have, for a hero! of 1,000 sheep, 
2,000 ticks per month during the tick season. Each female means 
about 4,000 larvae. This would make 8,000,000 larvae, which is a 
rather large number, though it is of course impossible to estimate 
what percentage of these would ever reach maturity. It might, how- 
ever, be possible to eliminate the sheep which are likely to breed the 
majority of the ticks. . Could this be done, it would be possible to 
use sheep in the destruction of ticks without dipping them. Until 
that fact is demonstrated, however, it would seem necessary to dip 
sheep along with other live stock in case they were allowed to run in 
" ticky " country. Even if it were not necessary to dip sheep with heavy 
wool, it would certainly be necessary to dip lambs or sheared sheep. 
A mere glance at the table will show that lambs or sheared sheep will 
breed a considerable number of ticks and kill but few. The only pos- 
sibility, therefore, of employing sheep in the work of tick eradication 
would be the using of wethers of other sheep with heavy wool. It 
does not appear practicable to attempt to use wethers alone, under 
any circumstances, as a means of ridding the Bitter Root Valley of 
spotted fever ticks. Nevertheless it would appear to be possible to 
use sheep as one means of reducing the numbers of the ticks, although 
in this connection several considerations must be mentioned. 
