TEXAS FEVER 297 



fact has limited the improvement of the Southern cattle by 

 the introduction of pure bred animals from the North. 



Eradication. It is, of course, impossible to allow the free 

 shipment of tick-infested cattle into the Northern States, 

 where they would be brought in contact with susceptible 

 animals. Before the nature of the disease was recognized, 

 such shipments made in the summer caused great losses in 

 Illinois and Indiana. In 1891 the Texas-fever line was 

 established, marking the boundary between the sections free 

 from the transmitting tick and those in which it is still 

 present. The line is not a fixed one, but changes from year 

 to year a< the work in tick eradication progresses. The 

 methods formerly used to free the cattle from ticks were 

 based on the life history of the insect. The female deposits 

 her eggs on the ground. The shortest period required for 

 Ihr eggs to hatch is twenty days. The young ticks thai d< 

 not succeed in attaching themselves to an animal die from 

 starvation. The period required to insure the destruction 

 of the ticks by starvation is dependent on moisture and 

 temperature conditions. In general, moisture and cld 

 prolong while dry ness and heat shorten the period the ticks 

 will live on a pasture. This period is important, since one 

 of the ways of freeing cattle from ticks is to place them on 

 one pasture for a short period, then on another, and not 

 return them to the first until starvation has destroyed the 

 ticks. 



By a proper rotation on tick-free pastures the cattle can 

 be freed from t icks. The cattle must not be allowed to re- 

 main on one pasture longer than twenty days, since this is 

 the shortest time in which the young ticks appear after the 

 females have dropped from the cattle to lay the eggs. This 

 method is a long and somewhat uncertain one to employ 

 when large areas are to be made free from the tick. It has 

 been largely supplanted by dipping the animals in a solu- 



