30 



Conclusion. — The immunity obtained from Tzaneen Virus of a lower 

 generation did not completely protect against the test of a higher 

 generation; even the immunity obtained from a Virus two or three 

 generations below that of the test was not complete. 



Immune Animals do not Act as Reseevoirs. 



It has experimentally been proved that the blood of an animal 

 suffering from horse-sickness is virulent during the febrile reaction and 

 only for a hmited time afterwards. This appUes of course only to 

 tests made by inoculation with blood from recovered animals, and 

 these have in all instances proved to be negative "if carried out almost 

 at any time after recovery up to a number of years, but the reservation 

 must be made here that under natural conditions, that is to say, through 

 the host, a transmission might occur from immune to susceptible 

 animals, a contingency which so far has not any support by analogy 

 with another disease. We are therefore entitled to conclude for the 

 present that the immune animal does not act as a reservoir. 



Serum op Recovered Animals. — In speaking of serum and virus in 

 horse-sickness, one has in the first instance to consider whether they are 

 adequate to each other, in other words, whether the serum used corre- 

 sponds to the same strain of virus with which the animal is injected. 



The serum of recovered animals has but little preventive value, but 

 acquires this when injected or infused in short or longer intervals as 

 already described. 



The observations refer to a virus which in the dose of 1 c.c. 

 subcutaneously injected is invariably fatal, and may be summarised as 

 as follows : — * 



(1) Adequate serum and virus mixture of equal quantities and 

 injected in multiples of the minimum dose, subcutaneously or intra- 

 jugularly, is, as a rule, harmless, but no immunity results. (2) Inadequate 

 serum and virus mixtures of equal quantities, mixed and injected 

 in multiples of the minimum dose are usually harmless. (3) The 

 inoculation of adequate serum previous to the subcutaneous injection of 

 virus, generally speaking, prevents the development of the disease ; the 

 same is sometimes observed when virus is injected intra jugularly ; no 

 immunity results. It is also sometimes noticed with inadequate serum 

 and virus. (4) The simultaneous inoculation of adequate serum and virus 

 does not prevent development of the disease in mules, and when the 

 doses of serum are properly adjusted, 98 per cent, of animals recover. 

 Under similar conditions recoveries in horses are less (about 60 per 

 cent.) ; when the dose of serum is increased all development may be 

 stopped. This refers also to some inadequate sera. The recovered 

 animals are immune. (5) Adequate virus injected previously to serum 



* Annual Report, U.V.B,, Trfinsvaal, 1904-05, 



