IMMUNIZING SUSCEPTIBLE CATTLE 25 1 



a native Southern animal or one which has recently been 

 rendered immune. 



When used in five cubic centimeter doses, blood from a 

 recently immunized animal gave a less virulent and less pro- 

 tracted form of the artificially produced fever than a similar 

 amount from a native. 



Two and one-half cubic centimeters of blood from a 

 recently immunized animal gave satisfactory results on two 

 imported Herford calves, aged eight and five months respec- 

 tively. Two cubic centimeters of the same blood acted satis- 

 factorily when injected in a one-month-old calf. Animals that 

 had been allowed sufficient time to perfectly recover from the 

 inoculation fever before being exposed on a tick-infested pas- 

 ture suffered no apparent ill effects from the ticks. Animals 

 exposed before convalescence was complete suffered a tempo- 

 rary relapse. 



The Experiment Station of that state offers to immunize 

 (free of charge) northern cattle, if they are shipped to the 

 state, for its stock raisers 



In Missouri, Connaway has immunized a few animals with 

 the blood serum from immune (Southern) cattle. This 

 method, however, needs further testing. In Mississippi, 

 Robert has tried the serum for both prevention and treatment 

 with somewhat similar results. In Virginia and Oklahoma 

 the disease and its prevention have been studied. In Texas, 

 Francis has conducted a number of immunizing experiments 

 with most excellent results. He has pointed out the value of 

 immunizing young (2 to 6 weeks old) calves by artificially in- 

 festing with ticks. In Australia the problem of immunizing 

 cattle against the effects of the spreading of the cattle tick in 

 order to save their stock from "tick fever" has become a matter 

 of serious consideration. 



The very limited knowledge of the life cycle of the para- 

 site of Texas fever precludes a satisfactory explanation of the 

 modus operandi in the production of immunity by these various 

 procedures. On this point there is need for much extended 

 investigation. 



