510 DISEASES OF CATTLE. 



a similar lajDse of time, always increasing the size of dose 50 per cent. 

 A thermometer, to indicate the course and severity of the disease, 

 is indispensable in this work. Usually, after 3 to 10 days, some- 

 times longer, the inoculated animals show a mild type of Texas fever, 

 which runs a course of from 6 to 8 days and is followed in about 

 30 days after the injection with a second attack of a milder char- 

 acter than the first. After 40 days, when the animal has entirely 

 recovered from the inoculation, a second injection may be given 

 to increase its immunity. In some cases a very severe type of fever 

 follows the first inoculation, requiring careful nursing and treatment, 

 as suggested above. A second, milder attack follows usually in about 

 30 to 40 days, after which the animal need have no further inocula- 

 tions. It is advisable to prevent any ticks from getting on the cattle 

 until 60 days after their inoculation or until they have fully recov- 

 ered, at which time a few ticks may be placed upon them in order to 

 reenforc« 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 during the late 

 fall or winter months, 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 a limited number of fever ticks upon their 

 bodies in order to produce the disease naturally. For this purpose 

 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, since the quantity 

 of germs injected can be more accurately regulated by means of a 

 syringe. 



