NINETEENTH-CENTURY MEDICINE 



the virus, which rapidly became attenuated when the 

 cord was dried in the air. The preventive virus, of 

 varying strengths, was made by maceration of these 

 cords at varying stages of desiccation. This cultiva- 

 tion of a virus within the animal organism suggested, 

 no doubt, by the familiar Jennerian method of securing 

 small-pox vaccine, was at the same time a step in the 

 direction of a new therapeutic procedure which was 

 destined presently to become of all-absorbing impor- 

 tance the method, namely, of so-called serum- ther- 

 apy, or the treatment of a disease with the blood serum 

 of an animal that has been subjected to protective in- 

 oculation against that disease. 



The possibility of such a method was suggested by 

 the familiar observation, made by Pasteur and nu- 

 merous other workers, that animals of different species 

 differ widely in their susceptibility to various maladies, 

 and that the virus of a given disease may become more 

 and more virulent when passed through the systems of 

 successive individuals of one species, and, contrariwise, 

 less and less virulent when passed through the systems 

 of successive individuals of another species. These 

 facts 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 transferred with curative effect to the blood of an 

 infected susceptible animal. Numerous experimenters 

 all over the world made investigations along the line of 

 this alluring possibility, the leaders perhaps being Drs. 

 Behring and Kitasato, closely followed by Dr. Roux 

 and his associates of the Pasteur Institute of Paris. 

 Definite results were announced by Behring in 1892 



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