TEXAS FEVER 299 



diseases, the information is not yet sufficiently complete, so 

 that effective measures can be carried out, or else the nature 

 of the diseases is such that there seems little hope of getting 

 rid of them in the near future. 



Immunization. The younir animal is not very susceptible 

 to Texas fever, and can be readily immunized by introduc- 

 ing into the blood a small number of the causal organisms 

 that will not produce a fatal form of the disease, but will 

 cause a sufficient degree of immunity to protect against 

 natural infection. The requisite number of organisms may 

 be introduced by transferring blood from an infected ani- 

 mal to the animal to be immunized. The amount of the 

 blood to be thus transferred depends on the susceptibility 

 of the animal. If an old animal is to be immunized, one 

 cubic centimeter of the blood is used, but if a yearling is 

 to be treated, three cubic centimeters of the blood may be 

 employed without danger. 



Again, the tick itself may be allowed to infect the ani- 

 mal, the number of organisms introduced being governed 

 by the number of ticks placed on the animal. The method 

 of immunization with blood is very successful, about 3 per 

 cent, being lost by vaccination and 7 per cent, by subse- 

 quent infection. The 10 per cent, loss, when compared with 

 the 90 per cent, loss that resulted when non-immunized 

 cattle were placed on tick-infested pastures, is a measure of 

 the success of the treatment . 



Certain cattle, as those of India, are resistant to the dis- 

 ease, and attempts have been made to breed strains that 

 possess such an immunity. 



Contagious abortion. The term abortion signifies the 

 premature discharge of the fetus. If the abortion occurs 

 late in the gestation period, so that the young may live, it 

 is often termed premature birth; there is, however, no es- 



