X. BACTERIAL VACCINES 



Historical. Early in the eighteenth century 

 attention was called to the fact that in Oriental 

 countries individuals were immunized against small- 

 pox by inoculating them with a little small-pox 

 virus under the skin. In 1796 Jenner showed that 

 similar immunity could be produced by inoculating 

 the virus of cow-pox, and this procedure was free 

 from the dangers that attended small-pox inocu- 

 lations. Following the discovery of the specific 

 microbe of anthrax, attention was directed to the 

 problem of combating this disease. Pasteur, who 

 had been greatly impressed with Jenner's work 

 with cow-pox, felt that attempts should be made 

 to produce a mild attack of the disease, and that 

 this would then protect against a virulent infection. 

 After considerable experimental labor he devised 

 the plan of inoculating animals with cultures of 

 anthrax which had been attenuated by being grown 

 at high temperatures, 43 C. These animals had 

 a mild attack of the disease from which they soon 

 recovered, and then were resistant to infection with 



virulent virus. Soon after this, inspired by Pas- 



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