THE STORY OF NINETEENTU-CENTURY SCIENCE 



Institute in Paris, and at the similar institutes, built on 

 the model of this parent one, that have been established 

 all over the world, in regions as widely separated as 

 New York and Nha-Trang. 



VI 



In the production of the rabies vaccine Pasteur and 

 his associates developed a method of attenuation of a 

 virus quite different from that which had been employed 

 in the case of the vaccines of chicken cholera and of an- 

 thrax. The rabies virus was inoculated into the system 

 of guinea-pigs or rabbits, and, in effect, cultivated in the 

 systems of these animals. The spinal cord of these in- 

 fected animals was found to be rich in 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 cultivation of a virus within the ani- 

 mal organism, suggested, no doubt, by the familiar J"en- 

 nerian 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 importance the method, namely, of so- 

 called serum-therapy, or the treatment of a disease with 

 the blood serum of an animal that has been subjected to 

 protective inoculation against that disease. 



The possibility of such a method was suggested by 

 the familiar observation, made by Pasteur and numerous 

 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 suc- 



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