TWENTY-FIVE YEARS OF BACTERIOL- 

 OGY: A FRAGMENT OF MEDICAL 

 RESEARCH 



(Address of the President of the American As- 

 sociation for the Advancement of Science, Chi- 

 cago, 1920) 



BY 



SIMON FLEXNER 

 Rockefeller Institute 



IMMUNITY 



JUST a quarter of a century ago, that is in 1895, the 

 announcement was made at the 67th meeting of the Ger- 

 man Society of Naturalists and Physicians that diphtheria, 

 one of the most severe and fatal diseases of mankind, had 

 been conquered by means of an antitoxin. This great 

 event is a landmark, not alone in the history of medicine, 

 but also in the history of the world, and it provides a high 

 peak of achievement from which the growth of bacteriol- 

 ogy may be viewed. In order that we may follow the 

 growth with understanding, it is necessary, at first, to 

 cast a glance backward before we begin on the narrative, 

 the aim of which is to bring us to the state of knowledge 

 of bacteriology existing in our own day. 



Since disease is so universal a phenomenon and com- 

 municability from individual to individual so obvious an 

 incident of its epidemic prevalence, the conception of a 



