PIROPLASMOSES ' 445 



placed on a non-infested pasture and all contact with tlcky 

 animals prevented. The original pasture is kept free from 

 animals until the following April when it will be free from 

 ticks. In the eight months during which the field has not 

 been used for pasture the seed ticks which hatch in the fall 

 have died of starvation, having bad no access to cattle. 



4. Feed-lot Method. — A field of corn or other forage crop 

 is fenced off into three different enclosures. Around each 

 enclosure a furrow is plowed and a board placed so as to 

 prevent the escape of ticks. The cattle are placed in this 

 field for a period of sixty days; spending twenty days in the 

 first enclosure, twenty in the second and twenty in the third. 

 At the end of this period they are free from ticks, as they were 

 not allowed to remain in any one of the enclosures long enough 

 for reinfestation. In moving the cattle from one enclosure 

 to another they should be driven over plowed ground and 

 after they are taken out the furrow should be sprayed with 

 crude petroleum. Obviously the cattle should not l>e fed 

 - hay nor given water from tick-infested pastures. 



Protective Inoculation. — Susceptible cattle shipped to 

 tick-infested regions, especially animals from six to eighteen 

 months old, may be immunized against Texas fever by one of 

 the following methods: 



1. The animals are confined in a tick-free enclosure and 

 a small number of (25 to 50) virulent seed ticks placed upon 

 them. A month later a greater number of seed ticks (2 to 

 400) is used. This will often produce a non-fatal type of 

 Texas fever which renders the animal immune to natural 

 infection. 



2. The susceptible young cattle are injected subcuta- 

 neously with the defibrinated blood of a native calf or a 

 recovered adult animal. Usually eight to ten days after the 

 injection the animal develops symptoms of anemia, hemo- 

 globinuria and sometimes bloody diarrhea. Microscopically, 

 the blood will show a great diminution of red blood corpuscles 

 and will contain a few piroplasms. In eight to ten days these 

 symptoms temporarily disappear but a month later usually > 

 a second reaction sets in which lasts only eight to ten days 

 but is milder in type, the red blood corpuscles showing only 



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