502 DISEASES OF CATTLE. 



reenforce their immunity. Naturally this time varies according to 

 the type of the attack. As the best results with these immunizing 

 experiments have been obtained in cool weather and with young 

 cattle, it is recommended that animals from 6 to 15 months old be 

 selected for inoculation, and that they be immunized late in the fall 

 or winter, in order that they may enter tick-infested pastures in the 

 spring without danger. 



By infesting with ticks. — Immunity may also be induced in suscep- 

 tible animals by placing limited number of fever ticks upon their 

 bodies in order to produce the disease naturally. For this purf)ose 

 only animals less than 1 year of age should be used, as the method is 

 not applicable for older and more susceptible animals. Upon the 

 bodies of these young cattle from 25 to 50 seed ticks should be 

 placed, which in the course of about 10 days will occasion a rise 

 of temperature and a mild form of Texas fever. When the animal 

 has entirely recovered from this attack, a second crop— double the 

 number first used — should be applied to the animal in order to in- 

 crease its power of resistance when pastured on infested soil. In 

 order to carry out this method successfully, a constant supply of seed 

 ticks must be at hand. This can be accomplished by placing the 

 mature females in a Mason fruit jar among some dirt and leaves and 

 keeping them in a warm place. In a few weeks the eggs will have 

 been laid and hatched, and a number of seed ticks will be present for 

 use in infesting the cattle to be immunized. By placing a few adult 

 females in the jar every two months there will always be a supply of 

 these young ticks. This method of producing immunity by controlled 

 tick infestation is not so safe as blood inoculation, as the number of 

 germs injected can be more accurately regulated by means of a 

 syringe. 



TREATMENT. 



When Texas fever has broken out, all animals, the sick as well as 

 the healthy, should at once be removed to a noninfected pasture. 

 While this may not cut short the disease, it may save the lives of 

 some by removing them from the possibility of attack by more young 

 ticks. Removal from infected pastures likewise prevents a second 

 attack, in October or early in November, which is caused by another 

 generation of ticks. It is true that sick natives infect with a new 

 generation of ticks the pasture to which they are removed, but these 

 usually appear so late that they have but little opportunity to do any 

 damage; hence, sick natives do not, as a rule, cause visible disease 

 in other natives. 



It is of importance to remove all ticks, so far as this is possible, 

 from sick animals, since they abstract a considerable quantity of 

 blood and thereby retard the final recovery. 



