INSECTS INJURIOUS TO DOMESTIC ANIMALS. ETC. 675 



they may infect the new host with the Texas fever at this stage, 

 even though they are so small as to be scarcely visible. 



Texas fever is caused by a minute protozoan animal of the same 

 general group as the parasite causing malaria (Bdbesia bigemina.) 



FIG. 594. Plan for freeing cattle and pastures from ticks by rotation, requir- 

 ing eight months, U. S. Dept. of Agr. 



It passes from the body of the infected female, no one knows just 

 how, into the eggs so that all her progeny are infective. Appar- 

 ently healthy cattle from permanently infected districts are usually 

 carriers of the disease but have developed immunity to the effects. 

 They are as dangerous as sources of infection for the ticks as are 

 the cattle sick with the disease. 



It has been definitely shown that the disease can not be trans- 

 mitted in nature in any way except by the bites of the infected 

 ticks. That being the case, the obvious way to eliminate the 

 disease is to destroy the ticks. The U. S. Department of Agri- 



