TWENTY-FIVE YEARS OF BACTERIOLOGY 117 



experimental investigation by him, is the aspect of Pas- 

 teur's labors to which I wish especially to direct your at- 

 tention, since it forms the connecting bond between the 

 earliest and thus the oldest, and the present and thus the 

 latest discoveries in a field in which medical science has 

 come to secure some of its most notable successes. There 

 can be no doubt that the discovery in 1880 of the artificial 

 immunity to fowl cholera came not as a direct incident, 

 but rather as an accidental circumstance to the experi- 

 ments being pursued. In after years Pasteur loved to 

 point out the importance of the "prepared mind" as a 

 requisite of the investigator, in order that he may seize 

 hold of and utilize in respect to a question propounded by 

 experiment what, viewed superficially, appears to be only 

 an indirect and misleading answer. The advances lead- 

 ing rapidly from the artificially induced immunity in fowl 

 cholera to the dramatic and historically and economically 

 important immunity in anthrax and to the humanly im- 

 portant immunity in rabies, involved no strictly new con- 

 ceptions on Pasteur's part. They consisted merely of the 

 carrying forward of the ideas, often ingeniously modi- 

 fied, derived from the study of the sources of the condi- 

 tion of immunity in fowl cholera. 



But should we inquire to what order of events already 

 known this phenomenon of artificial immunity belongs, / 

 we should say at once probably to the order having to do 

 with the Jennerian vaccination against smallpox. As 

 every one knows, vaccination against smallpox consists 

 in the utilization of human smallpox material which has 

 become modified by passing through the cow, in which it 

 sets up the condition named cowpox. When this modi- 

 fied microbic virus of the disease is returned to man, a 

 mild form of smallpox is induced, which suffices through 

 a term of years to protect the individual vaccinated, so- 

 called, from infection with the more active or virulent 

 smallpox virus. 



The significance of the new observations was grasped 



