26 



passed through immunisation within eight months previous to the infusion ; 

 those hyperimmunised a second or third time were done so after an interval 

 of three months to a year.* The longest period between immunisation 

 and hyperimmunisation was two years without breakdowns. The longest 

 period between immunisation and test with the same virus was six years. 



Conclusion. — The immunity obtained in mules by the s%multaneous 

 injection of serum and Ordinary Virus is complete concerning 

 quantity of Ordinary Virus with which it is tested ; concerning time, 

 it is so at least for six years. 



Immunity in Hokses. — No method of immunising horses has as yet been 

 introduced into practice. The horses referred to here have recovered 

 in experiments carried out for the purpose of finding such a method. 

 With a few exceptions the immunity obtained was due to the injection 

 of serum and virus in various combinations, but principally by simultaneous 

 injection. As this article deals with the immunity, the details of 

 immunisation does not enter within its scope. . All the recovered horses 

 were used for hyperimmunisation in a similar way as indicated in connec- 

 tion with the mules. Thus were hyperimmunised or otherwise tested with 

 Ordinary Virus 104 horses, amongst which were 10 hyperimmunised twice. 

 The amount infused for hyperimmunisation averages 8 to 10 litres. Five 

 horses were hyperimmunised three times. The intervals between hyper- 

 immunisation was usually short, averaging two to three months. The longest 

 interval between two hyperimmunisations was two years. The observation 

 was, that out of this number no horses showed a typical reaction due 

 to this test of hyperimmunisation. 



Note. — There was one horse which reacted with symptoms of dikkop. 

 At that time this occurrence was not understood. Soon after' the test 

 injection, the horse was grazed at Onderstepoort during the horse- 

 sickness season, and a new infection must have been contracted 

 naturally, a fact which will be explained later. 



Conclusion. — The immunity of horses obtained through the recovery from 

 an injection of Ordinary Virus is complete concerning quantity of 

 Ordinary Virus. Concerning time it is for at least two years. 



The virus used for hyperimmunisation and test did not correspond 

 in generation to that'^used for immunisation. The vira used principally 

 for immunisation were the fifth and the thirty-seventh generations, 

 counting every subsequent animal through which the ordinary strain had 

 passed as a generation. These animals were indiscriminately taken 

 amongst horses and jtnules, and did not follow each other with any 

 regularity. Only after the sixty-fifth generation the virus was continued 

 through horses exclusively. The greatest interval between the generation 



* Annual Report, G.V.B., Transvaal, 1906-07 — Immunisation of Mules with Ordinary Virus, 



