equine piroplasms in 38 cases out of 402 horses treated, and in 3 mules 

 out of 282, due to the infused blood, which kept the infection in a latent 

 form. 



A donkey foal kept for eighteen months out of the infection proved 

 to be virulent in the inoculation of 100 mules. It has been observed that, 

 similar to redwater, the injection of blood of immune foals is not so virulent 

 and that the majority of injected animals recover. This has been made 

 use of as a method of immunisation (blood of donkey foals). 



In this way were treated with horse foal blood : 34 horses, 27 donkeys, 

 and 135 mules. Three mules died of piroplasmosis. 



With donkey foal blood were injected : 80 horses, 81 mules, 15 

 donkeys. There were no deaths. 



Conclusion. — The blood of an equine which has recovered from an 

 attack of firoplasmosis remains infective. 



Test of Immunity by Injection of Blood. — A horse* which had 

 recovered from the disease in July, 1904, was tested by the injection of 

 2,500 c.c. blood of a horse which at that time was suffering from piro- 

 plasmosis, and containing numerous piroplasms. No reaction was noticed 

 in this horse. 



Of 35 horses immunised against piroplasmosis by injection of immune 

 blood, 3 horses died of piroplasmosis when hyperimmunised against horse- 

 sickness. 



Conclusion. — Immunity against Piroflasma equi may be broken 

 through infusion of large quantity of immune blood. {Horse-sickness 

 virus.) {Probably different strain.) 



Equine Pieoplasmosis as Complication of Other Diseases.— 

 In our experiments with horse-sickness, we frequently met animals 

 suffering from biliary fever whilst undergoing a horse-sickness reaction. 

 All possibilities of an artificial infection simultaneously with the injection 

 of serum or virus had to be excluded, since virus and serum were of old 

 standing. Similarly to what has been described in redwater is the case 

 here, a breakdown of immunity due to a concurrent fever. 



During the year 1905-06 these breakdowns were noticed during the 

 immunisation of 3,195 mules ; 26 showed piroplasmosis comp heated with 

 horse-sickness (0-8 per cent.), of which number 11 died (0-3 per cent.). 



Of 402 horses immunised against horse-sickness and passing through 

 a horse-sickness reaction, 12 showed complications with Piroplasma equi. 



Conclusion. — Immunity against equine piroplasmosis can be broken 

 when the immune animal is suffering from some other febrile disease. 



* Annual Report, a.V.B., Transvaal, 1904-05, page 104. 



