VACCINE-THERAPY 193 



become infected with the virus in a natural manner, that 

 pig is immune for life. 



It is therefore imperative for the successful immunization 

 of a herd of pigs that the virus of infection must be always 

 present, and without it no permanent immunity can be 

 conferred. 



The writer inquired of Dr. Poels what his experience 

 was of artificial infection in event of his failing to have 

 the means of natural infection — i.e., a diseased pig — at 

 hand, and his answer was, it was not serviceable, but that 

 he was experimenting by feeding pigs with the natural 

 virus, and was hopeful in time to overcome the present 

 difficulty of no natural infection, no immunity. 



The procedure adopted in Holland is this : When a pig 

 shows symptoms of swine fever, the whole herd is injected 

 with serum. The badly affected pigs are separated from 

 the slightly affected ones, and the experience of those in 

 authority is very favourable to serum therapy. In Dr. 

 Poels' words, " The slightly affected always recover ; the 

 very badly not often." 



Dr. Von Velseim's experience is that after the yearly 

 injection of 2,000 pigs, 6 to 8 per cent. die. 



In Holland there are no restrictions placed upon swine 

 fever areas, no compulsory notification, and no slaughter. 



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