33 



In the year 1907-08 about 200,000 sheep were vaccinated, the season 

 was a good one ; the only breakdown which occurred was in the Orange 

 River Colony affecting a ewe. 



In the year 1908-09 about 85,000 were inoculated, and about 80 

 breakdowns were noted in three different farms of three different districts 

 (Lydenburg, Ermelo, Piet Retief). 



Conclusion. — A certain number of breakdowns under natural conditions 

 are observed, even soon after vaccination ; these breakdowns vary in 

 their extent according to certain localities. 



The Blood of Immune Animals.— A number of sheep immunised six 

 to eighteen months ago were tapped, and the blood was injected in the 

 doses of 5 c.c. into susceptible sheep. In no instance were the lesions 

 of blue-tongue noted. 



When immediately afterwards tested on their immunity, with the 

 minimum doses of virus, these injected sheep proved to be susceptible to 

 blue-tongue. 



Conclusion. — Immune animals do not retain the infection in the blood. 



The same reservation as in horse-sickness has to be made here. 



Serum of Immune Animals. — Serum of hyperimmunised sheep was 

 tested on its preventive value, with the following results : — 



(1) Simultaneous subcutaneous injections of serum and virus, 



with the excess of the former, prevented all development of 

 disease ; intrajugularly injection was followed by reaction and 

 death. 



(2) Serum injected twenty-four hours previous to virus prevented 



the development of the disease. 



Conclusion. — The serum has preventive qualities. 



Resume. 



(1) Immunity in blue-tongue of sheep is never complete ; it can be 

 broken either by" virus of the same strain if applied in larger doses or by 

 a virus of a different strain. 



(2) The serum has preventive quahties, and immune animals do not act 

 as reservoir for virus. 



Heartwater. 



Heartwater is a specific disease of cattle, sheep, and goats, due to a 

 filtrable micro-organism present in the blood, which preserves its virulency 

 for not longer than forty-eight hours. Fresh blood of sick animals must, 

 therefore, be used as virus'. Any animal belonging to the genera men- 

 tioned above acquires immunity through the recovery from the disease. 



