INFECTION 



241 



as known the cattle tick {Bodphilus bovis)-'^ is the sole carrier 

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



cattle were freed from ticks 



ss?^ 



thev 



together 



Fig. 59. Sexually mature male 

 tick after the last moult, dorsal 

 viezv. {Sm-ith.) 



would not when kept 

 in small enclosures 

 transfer the disease to sus- 

 ceptible animals, but that 

 when susceptible cattle became 

 infested with the ticks either 

 b}' grazing in infested pastures 

 or by having placed upon them 

 young ticks hatched in the lab- 

 oratory the disease appeared.! 

 The infection 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 carr}' 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 cycle maj' be assumed to begin at once. 



*This tick was first described by C. V. Riley in 1S6S as Ixodes bovis. 

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

 Tick, Journ. Comp. Med. and Veterinary Archives, July, 1891, Jan., 1892) 

 and gave it the generic name of Boop/it I us (ox loving). This seems to 

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

 fever. 



•fit is interesting to add the results of an experiment conducted by 

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

 neviessity 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. 



