DISEASES OF FARM ANIMALS 261 



tary arrangements and by vaccination. Where the 

 cattle are infected with the tick, the ticks can be 

 killed by smearing the animals with a solution 

 capable of killing the ticks without harming the 

 cattle. In large herds a large vat of crude petrol- 

 eum is used to immerse the cattle in. In small 

 herds smear the cattle with a mixture of equal parts 

 of cottonseed oil and crude petroleum. 



How to rid the pastures of the tick without kill- 

 ing the vegetation on them has for a long time been 

 the problem. Divide the pasture in two parts by a 

 double parallel line of fence with a lo-foot space 

 between, to prevent ticks from crawling across. 

 One of these pastures is then kept free of cattle for 

 two winters and one summer. After the second 

 winter it will be free of ticks and ready for tickless 

 cattle, when the other pasture is abandoned for the 

 same time. 



Vaccination is for the purpose of immunizing 

 cattle that are brought from a non-infected district 

 to an infected district. Calves about six to eight 

 months old should be used, as they are more im- 

 mune than adult cattle. The immunity is caused 

 by introducing the germ into the blood in a weak- 

 ened form. This may be done in two ways — ^by 

 placing virulent young ticks on the calves or by 

 artificial vaccination. When this is practiced, it 

 should be done in two or three inoculations, as it 

 gives better results. The intervals should be about 

 three weeks. The amount of virulent blood should 

 be small the first time and increased in the follow- 

 ing treatments. 



The inoculation always results in a more or less 

 serious attack of the fever upon the animal treated. 

 Some may die, but the proportion of deaths' result- 

 ing artiong animals taken directly into the infected 



