242 



TEXAS FEVER 



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Fig. 6o. Pliotograph of atiiinal sick zvith Texas fever. 

 graphed bv Connaway). 



[Photo- 



1. Adult ticks drop to the ground in from i to 3 days 

 after the infested cattle are placed in the field. 



2. Adult ticks lay their eggs in about 7 days after drop- 

 ping to the ground. 



3. Eggs are hatched in about 20 days after they are laid. 



4. Young ticks crawl upon cattle from i to several days 

 after the}^ are hatched. 



5. In about 10 days from the time the young ticks crawl 

 upon the susceptible cattle the rise of temperature appears. 



The length of time that must elapse (period of incubation) 

 from the exposure of susceptible cattle to the development of 

 the disease depends on whether or not the whole life cycle of 

 the tick must be passed or part of it has alread}' gone by. 

 If susceptible animals are placed in a pasture where the young 

 ticks are just ready to crawl upon them the infection of the 

 cattle is accomplished at once and the high fever appears in 

 about ten days, practically the minimum time. It has been 

 experimentally demonstrated that the young ticks are able to 



