cs 
332 TEXAS FEVER 
animals consists therefore in first infesting them with the cattle tick.* 
The number of ticks necessary to carry the disease is small so that 
frequently they will not be observed unless the sick animals are care- 
fully examined. The life cycle of the tick will, therefore, explain the 
variation in the time elapsing between the exposure of northern to 
southern cattle and the appearance of the disease. Starting with tick 
infested animals placed with native cattle in a northern pasture the 
adult female ticks 
drop to the ground 
almost daily, so that 
the following life cycle 
may be assumed to 
begin at once. 
Adult ticks drop to 
the ground in from 1 
to 8 days after the in- 
fested cattle are 
placed in the field. 
Adult ticks lay 
their eggs in about 
7 days after drop- 
ping to the ground. 
Eggs are hatched 
in about 20 days 
after they are laid.t 
Young ticks crawl 
upon cattle from 1 to 
Fig. 81. CATTLE TICKS ON AN INFESTED ANIMAL several d ays after 
after Mohler), they are hatched. 
In about ten days from the time the young ticks crawl upon the 
susceptible cattle the first symptom, a rise of temperature, appears. 
The length of time that must elapse (period of incubation) from the 
*It is interesting to add the results of an experiment conducted by Dr. Cooper Curtice 
in the Bureau of Animal Industry which shows the necessity of the tick in inoculating 
cattle. Ina tick infested district in the south, a field was cleared of ticks by fencing and 
keeping cattle off fora year. Susceptible northern cattle were transported to and placed’ 
in this field where they thrived for a season. The second year they were placed in a 
second cleared pasture where they kept well for another year. The third year they 
were placed in a tick infested pasture where they died promptly of Texas fever. 
{Mohler states that the time required for the hatching varies from 13 days to six 
weeks, depending upon temperature, moisture, soil, etc. He states further that the 
eggs may remain dormant for several months. 
