INFECTION 



243 



travel for a consider- 

 able distance in a 

 pasture. In pasures 

 where tick infested 

 cattle are grazing, 

 young ticks are very 

 liable to be on the 

 ground continuously. 

 In est i m a t i n g the 

 time to elapse after 

 the exposure to the Fig. 61. Sexually malurc female after 



tick infested field the last tnoult, dorsal view. (Smith.) 

 before the disease will appear, it is necessary, therefore, to 

 determine the exact stage in the life circle of the ticks at the 

 time when the animals come in contact with them. 



Small quantities of the blood from immunized cattle in the 

 tick infested district, when injected into susceptible animals 

 either intravenously or beneath the skin, will produce the 

 disease. While this mode of infection rarely if ever occurs in 

 the natural order of events, it may happen that in case of cer- 

 tain operations bits of blood may be carried directly from a 

 southern to a northern animal thus inoculating the latter with 

 the disease. 



In the fall of 

 1898 two cases oc- 

 curred in the prac- 

 tice of Dr. Ambler 

 of Chatham, N. Y. 

 The owner had his 

 animals dehorned 

 in December and 

 soon afterward two 



<5 



Fig 62. 



(Smith.) 



Eggs and young tic/;, just hatehed. 



fatal cases of Texas fever developed. The Piroplasma and the 

 characteristic lesions were present. Inquiry revealed the inter- 

 esting fact that the two animals which sickened and died were 

 dehorned immediately after two imported Southern cattle. The 

 owner was not aware of the fact at the time that these were 



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