190 VETERINARY STUDIES 



Method.^ — The usual process consists in drawing blood from 

 the jugular vein of an animal (not less than two years old) that 

 was infested with ticks the preceding summer, and injecting it 

 under the skin of the animal to be inoculated. This will pro- 

 duce tick fever, usually in a mild form in from three to ten 

 days. Not more than about three per cent will die from this 

 inoculation if the subjects have been selected with proper care 

 and are judiciously handled. About 5 to 7 per cent are im- 

 perfectly immunized. 



Tlie dose varies from 1 to 3 c.c, depending on the age of the 

 animal. Young cattle take the larger dose and older cattle 

 the smaller. Cattle that do not show plain reaction, fever, de- 

 pression, etc., should receive a second or even a third treat- 

 ment, each dose being 50 per cent larger than the preceding 

 and given at intervals of about 40 days. Young cattle less than 

 one year old may be immunized by the use of young seed ticks 

 but this method is not recommended where the blood-inoculaticn 

 method is available and is not at all suitable for older cattle. 



Important conditions. — The animals should be between six and 

 fifteen months old. Older cattle may be treated, but they are 

 less conveniently handled and results are less satisfactory. 



The inoculating should preferably be done during December, 

 January, or February, for tick fever is less severe in cold 

 weather. 



All ticks should be kept off the inoculated cattle for about 

 60 days or until they have fully recovered from the inoculation 

 fever. 



The inoculated cattle may then be protected for a time from 

 gross tick infestation by having their legs and under parts of 

 their bodies greased. A few ticks after the cattle have fully 

 recovered from inoculation are useful as they reinforce the 

 immunity. 



Inoculated animals on infected premises should be infested 

 with the first crop of ticks appearing in the spring, for these 

 are probably less virulent than those hatched in the fall, and 

 therefore produce a milder type of disease. 



In the opinion of the writer the best method of introducing 

 jiure-bred animals for improvement of the native stock is to 



' See also Federal Bureau of Animal Industry and State Ag^rieultural 

 Experiment Station bulletins on Texas Fever for additional details of 

 vaccination. 



