INFECTION 241 



as known the cattle tick (^Bo'ophilus bovisf-' is the sole carrier 

 of the parasite. It was pointed out by them that when southern 



cattle were freed from ticks 

 they would not when kept 

 together in small enclosures 

 transfer the disease to sus- 

 ceptible animals, but that 

 when susceptible cattle became 

 infested with the ticks either 

 I by grazing in infested pastures 



Fig. 59. Se.vua/ly iiialure male or by having placed upon them 

 tick after the last moult, dorsal young ticks hatched in the lab- 



vieiu. [Smith ) * ^.u j- j x 



' oratory the disease appeared.! 



The infectiou of Northern cattle with Texas fever by 



Southern animals consists therefore in first infesting them with 



the cattle tick. The number of ticks necessary to carry the 



disease is small so that frequently they will not be observed 



unless the sick animals are carefully examined. The life 



cycle of the tick will, therefore, explain the variation in the 



time elapsing between the exposure of northern to southern 



cattle and the appearance of the disease. Starting with tick 



infested animals placed with native cattle in a northern pasture 



the adult female ticks drop to the ground almost daily so that 



the following life C)'cle may be assumed to begin at once. 



*This tick was first described by C. V. Riley in 186S as Ixodes bovis. 

 Later, Cooper Curtice investigated this parasite (Eioiogy of the Cattle 

 Tick, Journ. Comp. Med. and Veterinary Archives, July, 1891, Jan., 1S92) 

 and gave it the generic name of Boophil us (o:s. loving). This seems to 

 be the only species of cattle tick which transmits the parasite of Texas 

 fever. 



tit is interesting to add the results of an experiment conducted by 

 Dr. Cooper Curtice in the Bureau of Animal Industry which shows the 

 necessity of the tick in inoculating cattle. In a tick infested district in 

 the South, a field was cleared of ticks by fencing and keeping cattle off 

 for a year. Susceptible northern cattle were transported to and placed 

 in this field where they thrived for a season. The second year they were 

 placed in a second cleared pasture where they kept well for another 

 year. The third year they were placed in a tick infested pasture where 

 they died promptly of Texas fever. 



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