DISEASES OF CATTLE 341 



be carefully sterilized. Farmers' Bulletin, No. 206, gives 

 details of the method. 



303. Black-Leg. This is a very serious infectious disease 

 caused by a certain bacillus. It is not transmitted by 

 direct contact, but comes from infected soil. Animals 

 that die from it should be burned. The losses from this 

 disease have been very serious and widespread. Vacci- 

 nation will prevent most of the loss. A vaccine for this 

 purpose is furnished by the United States Department 

 of Agriculture. 



304. Texas Fever. One of the most serious obstacles 

 to the development of the live-stock industry in the South 

 is the Texas fever. The direct cause of the disease is a 

 microscopic animal parasite (protozoan) that lives in 

 the blood. But it is not transmitted directly from one 

 animal to another. It lives a part of its life in the body of 

 the cattle tick. Cattle contract it from the ticks and in 

 no other way. The parasite passes a part of its life in the 

 cow and a part in the tick. This is similar to the method 

 in which malaria and yellow fever are transmitted to 

 people by means of mosquitos. 



Cattle that are born in the South usually become 

 immune to the disease by infection when calves. When 

 northern cattle are taken South, they almost invariably 

 die with the disease. When southern cattle are driven 

 North, they mark their passage by killing the northern 

 animals with the disease. For many years the southern 

 states have been quarantined for this reason. 



Northern cattle, taken South, are sometimes inoculated, 

 so as to produce mild cases and cause immunity. Another 

 method that is now being tried is to eliminate the ticks. 



