62 The Farmer's Veterina/nj Adviser. 



fatal disease, which would prove vicarious of the more severe 

 form. 



One drawback to this method is that, if applied to a virus 

 whicli has been some time removed from the system and has 

 produced spores, the latter still retain their potency. 



XIV. IMMUNITT BY INOC0LATION WITH TIEUS WEAKENED BY 



EESTrSTQ INACTIVE (sTAEVED) IN FREE CONTACT WITH AIE. 



This is the far-famed method of the brilliant Pasteur. 

 He began his work on the virus of chicken-cholera, setting 

 aside his cultures of the virus in vessels unfurnished with 

 any more food for their nourishment and freely exposed to 

 the air. After a sufficiently long exposure he found that 

 the virus had lost somewhat of its deadly character, and 

 after a three months' rest it could be inoculated on healthy 

 fowls without a fatal result, and proved protective against 

 another attack of the disease. Later, with anthrax virus 

 cultivated in chicken-soup at 41° C, so that it would not pro- 

 duce the unimpressible spore, he produced by delay a debil- 

 ilated virus which could be safely inoculated on healthy 

 sheep and cattle, and would protect them from a second at- 

 tack. Later still the method has been successfully applied 

 to canine madness and other diseases. The one great draw- 

 back to the method is the fact that, though the individual is 

 preserved, yet the virus is multiplied in its system and scat- 

 tered in the surroundings, ready to resume its virulence at 

 any time under favorable circumstances. Pasteur himself 

 has secured this reversion to the deadly type by inoculating 

 the weakened virus of fowl-cholera on the chick, and suc- 

 cessively on older and older animals. It is easy to conceive 

 how a diffusion of germs, by a general inoculation with the 

 weakened virus, may become the means of starting many 

 new centres of deadly infection. 



Pasteui-'s system is therefore not one that can be adopted 



