CENTURY'S PROGRESS IN SCIENTIFIC MEDICINE 



cessive individuals of one species, and, contrariwise, less 

 and less virulent when passed through the systems of 

 successive individuals of another species. These facts 



LOUIS PASTEUR 



suggested the theory that the blood of resistant animals 

 might contain something directly antagonistic to the 

 virus, and the hope that this something might be trans- 

 ferred with curative effect to the blood of an infected 

 susceptible animal. Numerous experimenters all over 



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