592 Veterinary Medicine. 



stantly obtruded itself that casual cases were never found in the 

 absence of the tick. Finally, in 1889, Kilborne conceived the 

 idea of putting the matter to the test, and with the approval of 

 the Chief of the Bureau of Animal Industry, set aside special 

 paddocks for this purpose. Five native cattle were placed, at 

 midsummer, with three South Carolina cattle, from which all 

 ticks had been carefully picked, and they completely escaped 

 infection. 



After seventy-one days, on September 6th, when the hottest 

 weather had passed, two were turned into a lot with four South 

 Carolina cattle of the original herd which had stocked the pasture 

 with ticks. Of the two, one died of Texas fever, September 20th, 

 and the other sickened in the last week of September, and had a 

 relapse in October, but finally recovered. Of eleven other native 

 cattle placed in this tick-infe.sted field up to September 30th, ten 

 sickened and one escaped. One animal placed in the fi^eld Octo- 

 ber 19th escaped. 



Again three North Carolina cattle and three natives were placed 

 in a field September 14th and 15th. The new generation of ticks 

 was retarded by the cool season, so that few larvae appeared on 

 the native stock yet one of the three sickened. 



These results were confirmed by a series of other similar ex- 

 periments. 



In a further experiment, September 13th, thousands of ticks, 

 mostly mature, from North Carolina, were scattered over a sound 

 lot and four native cattle turned into it next day. Three sickened 

 and one, to outward appearance, escaped. 



These results- were corroborated by experiments made in suc- 

 ceeding years. In addition the disease was produced regularly 

 in native stock by placing on their skin the six-legged larvae of 

 boophilus bovis, which had been hatched in glass vessels in the 

 laboratory. It was also shown that the Washington winter de- 

 stroyed the ticks in infected pastures so that native cattle could 

 be safely turned on them the following spring or summer. 



To summarize : — 



1 . The blood of southern cattle containing the piroplasma pro- 

 duced the disease when injected into a healthy susceptible ani- 

 mal. 



2. The animal with piroplasma in its blood, did not convey the 



