LIFE histoid OF CATTLE 'nek. 27 
PARASITIC PERIOD. 
The data already given regarding the periods of preoviposition, 
incubation, and survival of seed ticks have an important bearing on 
the time required to free pastures or other inclosures from ticks pro- 
vided tfu cattlt an removed. The data given under the present head- 
ing, on the other hand, show the time required at different seasons 
to fret cattli <>i ticks by 'placing them in inclosures from which thi ticks 
havi been eliminated either by systematic starvation or by tin ust <>/' 
naturally tick-fret areas } as, for instance, fields that havt been in culti- 
vation for om crop st ason. 
In this work we have utilized a grade Durham steer, 17 months 
old at the beginning of the experiments. (See PI. [I, fig. 1.) By 
means of kerosene emulsion he was carefully cleaned of the thou- 
sands of ticks infesting him when obtained. Thereafter he was thor- 
oughly washed to remove traces of the insecticide and hundreds of 
seed t icks were applied. Under proper precautions to avoid the steer's 
accidental infestation, these ticks were allowed to reach maturity. 
After the ticks of, each infestation became adult the steer was thoroughly 
cleaned and placed in another inclosure, which in each case had been 
carefully disinfected by means of sprays. This prdcess has now been 
repeated until ten infestations have been reared covering the period 
between August, 1905, and March, 1907. The details are given in 
Table VII. In rotation systems the minimum developmental period 
is the most import ant, because the cattle must be removed before 
the earliest developed ticks have had offspring to reinfest them. 
Therefore special reference is made in the table to the shortest periods 
found, although the longest and the average are both given. 
OCT o o 
The following deductions may be made from this table: 
1. The period from attachment to dropping ranges from 21 to 58 
days. It should he noted that in the longest periods the limit was 
reached by only one or- two belated ticks, the majority approaching 
the average. 
2. The average period ranges from 26.5 to 43 days. 
3. The average parasitic period is normally some days longer in 
winter than in summer. But warm winter weather, as happened in 
infestation No. 9, may reduce the period even below the average for 
the summer. 
A. The slowest developing t icks of one infestation may occupy from 
H) days (in the summer) to 32 days (in the winter) longer than the 
most rapidly developing ones. The rapidity of development of the 
ticks of the same infestation depends somewhat upon their location. 
Those on the portions of the body where the blood supply is most 
abundant develop most quickly, [ngeneral it seems that heavy infes- 
tations develop a little more quickly than light ones. This maybe 
