464 VETEKINAEY HYGIENE 



Methods of Producing Active Immunity. 



1. Immunity may be produced by the inoculation of a 

 pure virus ; for example, pleuro-pneumonia and sheep- 

 pox. 



2. By attenuated virus obtained by heating and drying ; 

 for example, anthrax, quarter-evil and rabies. 



3. Attenuated virus obtained by passing it through other 

 animals ; for instance, swine erysipelas, and tubercu- 

 losis (?). 



4. By attenuation from unknown causes, of the virus 

 occurring in the body of the sick or recovered animal ; 

 for example, rinderpest bile, and the blood of recovered 

 cases of Texas fever. 



5. By sero-virus inoculation, either simultaneously or 

 successively mixed ; for example, rinderpest, swine ery- 

 sipelas, sheep-pox, quarter-evil, malarial catarrhal fever of 

 South African sheep, and South African horse sickness. 



Methods of Obtaining Passive Immunity. 



The production of passive immunity is a valuable thera- 

 peutic measure, in those diseases in which the organisms 

 cannot live long apart from the animal body ; for example 

 rinderpest, where the virus scarcely lives three days apart 

 from the body. Passive immunity may be produced by 

 the injection of varying quantities of serum taken from an 

 immunised animal. Large quantities have to be employed, 

 but this measure tides over the critical period, and saves 

 the remaining animals of the herd from getting infected. 

 Much the same procedure may be used in sheep-pox when 

 the outbreaks are isolated ; it has also been suggested for 

 foot and mouth disease, and swine plague (Schweine- 

 seuche).* 



For the latter disease a polyvalent serum is employed 

 made by injecting into the animal to be immunised several 



* This is not the swine fever of Britain. 



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