PREVENTION 249 



§ 185. Differential diagnosis. Texas fever is easily 

 differentiated from other disorders or infectious diseases by the 

 presence of its specific parasite. 



In the absence of a suitable microscope the differentiation 

 can in most cases be made from the character of the lesions, 

 the history of the animals, the presence of the cattle tick and 

 the course of the disease. The lesions are not simulated by 

 any other disease of cattle, although the enlarged, dark spleea 

 may suggest anthrax and in a hasty diagnosis the two may be 

 confused. From the fact that all animals exposed together 

 usually come down with the disease together poisoning may 

 be suggested, but here again a study of the symptoms and 

 lesions are sufficient to eliminate toxic disorders. 



§186. Prevention. The discovery of the specific cause 

 of Texas fever and of the cattle tick as the common means of its 

 transmission has reduced the preventive measures to a direct 

 warfare against the tick. The National Government has 

 determined the territory in which the tick naturally exists and 

 from which cattle, on account of the parasite, cannot be 

 shipped to uninfected districts, except under certain very 

 restricted conditions. (See regulations for transmission of 

 cattle p. 618, Report of the Bureau of Animal Industry for 

 1898.) Likewise susceptible northern cattle cannot be trans- 

 ported to the infested districts (south of Texas fever line) 

 unless they can be placed in fields that have been freed from 

 ticks. The elimination of the disease depends therefore, upon 

 the elimination of Bo'dphilus bovis. While this may be im- 

 possible in the territory of large ranches, there seems to be no 

 reason why in the dairy districts of the South it cannot be 

 accomplished. 



^ 187. Immunizing susceptible cattle. A number 

 of investigations have been undertaken directed toward the 

 development of methods for immunizing northern cattle 

 against Texas fever in order to enable the shipment, especially 

 of breeding stock, into the south. In 1895, the writer in con- 

 junction with Dr. E. C. Schroeder, began an immunizing 

 experiment which v/as continued and reported by Dr. Schroeder 

 in 189S. 



