38 



higeminum undergoes a further multiplication process and leads to the 

 appearance of redwater complicating the former disease. Statistics for the 

 year 1903-04 show that of blood smears sent to the laboratory for diagnostic 

 purposes : — 



311 were pure East Coast fever infections ; and 23 complicated with 

 redwater. 

 Statistics for the year 1904—05 show : — 



334 pure East Coast fever infections ; and 16 compHcated with 

 redwater. 

 Statistics for the year 1905-06 show : — 



152 pure East Coast fever infections ; and 5 complicated with 

 redwater. 

 Statistics for the year 1906-07 show : — 



133 pure East Coast fever infections ; and 5 complicated with 

 redwater. 

 Statistics for the year 1907-08 show : — 



239 pure East Coast fever infections ; and 6 complicated with 

 redwater. 



Conclusion. — Immunity against redwater, can he broken when the 

 immune animal is suffering from some other febrile disease. (It is 

 possible that the cases of breakdowns noted by me in Texan 

 and Madagascar cattle, shortly after a railway journey, were due 

 to this.) 



EOUINE PiROPLASMOSIS. 



This disease is due to the introduction of Piroflasma equi into sus- 

 ceptible equines, either naturally by the bite of the red tide {JRhipicefhalus 

 evertsi) or artificially by inoculation of blood containing this parasite. 

 The blood retains its infectivity for a Umited time, about three weeks in 

 our experiments. Animals which recover from the natural or artificially 

 contracted disease may show more than one reaction.* The recovery 

 means immunity. Horses born and bred in the Transvaal veld become 

 immune by the na.tural tick infection. Foals suffer but little from the 

 disease. 



Blood of Immune Animals. — Experiments undertaken to this effect 

 have demonstrated that the blood of immune horses is infective for 

 horses, mules, and donkeys, and vice versa. The blood of a zebra 

 caught in the bushveld proved to be infective for horses. 



An immune animal retains the infection probably for a hfetime when 

 exposed to ticks, and for a considerable time when not exposed. 



In our experiments for the purpose of hyperimmunisation in horse- 

 sickness by transfusion of blood from sick to healthy horses^ we noted 



"Annual Report, G.V.B., Transvaal, 1903-04. 



