HISTORIC DEVELOPMENT OF IMMUNOLOGY 29 



duced by Pasteur depend on active immuniza- 

 tion with attenuated living virus. By this means 

 he was able to control three of the epizootic dis- 

 eases prevalent in France, and to reduce the 

 mortality of rabies in man to a minimum; but, 

 unfortunately, it has not been possible to extend 

 the application of this principle materially, and 

 all important advances have since been made 

 with other means of active immunization. Pas- 

 teur's method of inoculation is the basis of the 

 various forms of protective and therapeutic in- 

 oculation or vaccination in use at the present 

 day, whether the vaccine consists of a living 

 culture of modified virulence, or a suspension of 

 the killed microorganisms, or an extract of pol- 

 len grains which are the causative factors of 

 hay fever. 



It was shown by Salmon and Smith in 1886, 

 and independently by Chamberland and Boux 

 in the following year, that it was not necessary 

 to introduce living microorganisms in order to 

 produce immunity, but that the same result 

 could be obtained by injecting bacteria killed by 

 heat or, in some cases, by injecting culture fluids 

 from which the bacterial cells had been removed 

 by filtration. 



