'A9. 



of the same strain, and again an injection of 100 c.c. another 33 days 

 later caused a typical reaction. A lamb which had contracted blue-tongue 

 and recovered from an injection of virulent blood showed typical lesions 

 of blue-tongue when injected 71 days later with 60 c.c. virulent blood of 

 the same strain. A number of sheep injected with increasing doses of 

 virulent blood for the purpose of hyperimmunisation generally show 

 fever reactions after the first and second injection. In later injections 

 these reactions are no longer noticed. The fact is noteworthy that when 

 the hyperimmunisation is carried out soon after immunisation no deaths 

 result from this increasing amount of blood. The reaction becomes the 

 more pronounced the later the injection of virus is carried out after 

 immunisation. 



Of 40 sheep tested with 20 c.c. virus four and seven months after 

 vaccination, severe fever reactions were noticed in .15 sheep and shghts 

 reactions in 14 sheep ; in some of these typical symptoms of the disease 

 were noticed, and 1 actually died as a result of it. 



Conclusion. — Immunity against hlue-tongue conferred by virulent or 

 attenuated virus is not complete. It may he broken with a larger 

 quantity of the same strain of virus, and this breakdown is more 

 certain to occur the longer the period which elapses between im- 

 munisation and test. 

 The breakdowns of immunity in the majority of cases do not end with 

 death. 



Experience in Practice. — The vaccination of sheep was introduced 

 into practice in 1907, and during the time when blue-tongue was rampant. 



The mortality within the first fourteen days after inoculation may 

 principally be accounted for by natural infection. In the 5,875 sheep, 

 of which records were kept, the disease stopped after this period ; the 

 mortality amounted to 7 animals, equal to 0"4 per cent. Of 16,218 

 susceptible non-treated sheep running under the same conditions as above, 

 1,817 died' of blue-tongue, or ll.v"per cent. 



Conclusion. — The vaccination of sheep during an epidemic of blue- 

 tongue stops the disease after fourteen days, and the sheep remain 

 immune for the rest of the season. 



The post-mortem examinations of seven sheep mentioned in the 

 foregoing notes out of the vaccinated number could not be controlled ; 

 thus some doubt as to correct diagnosis does exist. However, in the 

 same season amongst the sheep belonging to the laboratory exposed on 

 the notorious farm Onderstepoort, some breakdowns were noted, of which 

 the particulars are as follows : — 



One sheep contracted spontaneous blue-tongue ten months, a second 

 one eight months, a third one fourteen months, and a fourth one fifteen 

 months after immunisation. 



