41 



The Blood of Immune Dogs is infective and, contrary to tiie other 

 piroplasmosis, such blood is as virulent both for young and old animals 

 as is that of sick animals. The blood of an immune dog retained its 

 infectivity in our experiments during one year. 



Robertson* quotes an instance of thirteen months and another of 

 two full years. JRobertson was able to infect this latter dog again by 

 injecting virulent blood. 



Conclusion. — Immunity against canine piroplasmosis is present as 

 long as the dog retains the infection in the blood ; when this ivears off 

 then it again becomes susceptible. Under natural conditions, this 

 will hardly be noticed, as the presence of ticks is the permanent cause 

 of re-infection. 

 Serum op _ Immune Animals. — The knowledge concerning the serum 

 of hyperimmunised animals can be summarised as followsf : — 



(1) The mixture of serum and virulent blood injected into suscep- 



tible dogs was haimless ; no immunity followed. 



(2) Injection of serum twenty-four hours before virus injection 



prevented development of disease ; no immunity followed. 



(3) Injection of serum twenty- four hours after virus prevented 



development of disease ; no immunity followed. 



(4) The serum was active in the way indicated both against a virus 



of a different animal (Heterologous), as against the virus 

 obtained from the serum supplying dog (Homologous). 

 Conclusion. — The serum of a dog hyperimmunised with virulent blood 



has preventive qualities. 

 Immunity in Inoculable Piroplasmosis. — Recovery from a piro- 

 plasmosis causes immunity. This immunity is not complete and can be 

 broken by virus of a different strain. The immune animals retain the 

 infection in the blood foi? a considerable length of time, and during this 

 time intercurrent maladies can break the immunity. The degree of 

 immunity varies somewhat in the various breeds of animals (redwater) ; it 

 seems to last as long as the blood remains infective (canine piroplasmosis). 

 The serum of hyperimmune dogs has protective properties. (Not tested 

 in redwater and equine piroplasmosis.) 



III.— SPIROCHAETOSIS IN CATTLE. 



Spirillum theileri causes in horses, cattle, sheep, and goats, a febrile 

 reaction of short duration, sometimes of a relapsing character and the 

 microscopical lesions of anemia. All animals suffering from a pure 

 infection recover. The infection is naturally transmitted by the progeny 

 of infected blue ticks, or artificially by the inoculation of blood containing 

 the parasites. 



* Jour. Comp. Path, and Therap., Vol. XIX, Part 2. 

 f Annual Report, G.V.B., Transvaal, 1903-04, 



