Ticks and Mites 



29 



the driving or shipping of southern cattle into 

 northern states. 



But for years the cause of this fever, which came 

 to be known as the Texas fever, was not known. 

 The southern cattle themselves seemed healthy 

 enough and it was difficult to understand how they 

 could give the disease to the others. It was early 

 noticed, too, that it was not necessary for the 

 northern cattle to come in direct contact with the 

 others in order to contract the disease. Indeed 

 the disease was not contracted in this way at all. 

 All that was necessary for them was to pass along 

 the same roads or feed in the same pastures or 

 ranges. Still more puzzling was the fact that these 

 places did not seem to become a source of danger 

 until some weeks after the southern cattle had 

 passed over them and then they might remain 

 dangerous for months. 



In 1886 Dr. Theobald Smith of the Bureau of 

 Animal Industry, United States Department of 

 Agriculture, found that the fever was caused by the 

 presence in the infected cattle of a minute Sporo- 

 zoan parasite (Piro plasma bigeminum). Further 

 investigations and experiments proved conclusively 

 that this parasite was transmitted from the infected 

 to the well animal only by the common cattle tick 

 now known as the Texas fever tick (Fig. 16). 



