364 TEXAS FEVER 



differentiated from other disorders of 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 spleen 

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

 contused. From the fact that all animals exposed together us- 

 ually 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. 



§ 272. 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 re- 

 stricted conditions. (See regulations for transmission of cattle, 

 p. 618, Report of the Bureau of Animal Industry for 1898). 

 Likewise susceptible northern cattle cannot be transported 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 elimina- 

 tion of Boophilus anmdatus. Recently the government has 

 undertaken to eliminate the ticks. Thus far the reports are 

 most encouraging. There seems to be no reason why in the 

 dairy districts of the South their eradication cannot be accom- 

 plished. 



^ 273. Immunizing susceptible cattle. A number of 

 investigations have been undertaken directed toward the de- 

 velopment 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 Schroeder, began an immunizing experiment 

 which was continued and reported by Schroeder in 1898. 



