Disease Transmission and Mans Resistance 



321 



Jenner's use of cowpox virus as an immunizing agent against small- 

 pox. He observed that milkmaids who contracted cowpox ap- 

 peared to be immune to dreaded smallpox. By rubbing or scratch- 

 ing cowpox vaccine into the skin of humans, they became immune 

 to smallpox. 



Fig. 55. The first vaccination to prevent smallpox. {From the 

 Fisher Collection of Alchemical and Historical Pictures.) 



Such vaccine is presently prepared by rubbing living cowpox 

 virus into scratches made on the shaved and disinfected abdominal 

 surface of calves. When typical eruptions develop in about a 

 week's time, the crusts are scraped off and the material in the 

 underlying lesions is harvested and suspended in 50% glycerol. 



