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BACTERIA PATHOGENIC TO MAN 



Statements in favor of the belief that one form 

 may be changed readily into another. 



6. Solid forms, approaching the atypical 



non-virulent forms, have been found 

 to be specifically virulent. 



7. The virulence of the diphtheria bacil- 



lus has been decreased artificially 

 with a change in form and cultural 

 characters, and slightly virulent 

 diphtheria bacilli have been made 

 more virulent. 



8. Non-virulent atypical bacilli have, 



in a few hands, been changed to 

 typical, specifically virulent diph- 

 theria bacilli. 



9. Virulent typical diphtheria bacilli 

 have been apparently changed to 

 solidly staining, non-virulent, diph- 

 theria-like bacilli. 



Statements opposed to this belief. 



Among large numbers of virulent diph- 

 theria no cultures have been found 

 which developed only solid varieties. 



Artificial decrease of virulence of the 

 diphtheria bacillus has not been accom- 

 plished easily, neither have slightly 

 virulent bacilli been made highly viru- 

 lent. 



Non-virulent atypical bacilli experi- 

 mented upon by most observers have 

 retained their characteristics on various 

 artificial culture media under different 

 conditions and in passage through 

 animals. 



Virulent diphtheria bacilli usually retain 

 their characteristics on artificial culture 

 media under different conditions. 



The central idea in the statements of those who believe that diph- 

 theria-like bacilli are simply transitory variations of the species bacillus 

 diphtheria is that both the diphtheria bacillus and those bacilli which 

 resemble them have many unstable properties, their form, their cul- 

 tural characteristics, their pathogenicity all varying within a wide 

 limit, so that one form may assume readily the properties of another 

 form. 



The separatists, on the other hand, have found that certain forms 

 possess such stable properties that one is not converted into another, 

 and hence they regard them as distinct species. 



In order to make a thorough test of this whole matter Dr. A. W. 

 Williams, of the Research Laboratory, undertook a careful investigation 

 of the subject. 



An outline of the work attempted shows the thoroughness of the 

 tests : 



1. A study of the diphtheria and diphtheria-like bacilli found in a 

 series of clinically typical diphtherias at the Hospital for Contagious 

 Diseases. 



(a) Serial smears of cultures directly from throats and noses. 

 (6) Pure cultures isolated from these cultures. 



2. A study of the diphtheria and diphtheria-like bacilli found in 

 healthy and diseased throats in a town during an epidemic of diphtheria. 



(a) Smears of cultures directly from throats. 

 (6) Pure cultures isolated from these cultures. 



3. A study of diphtheria and diphtheria-like bacilli found in sore 

 throats during an epidemic of diphtheria at a home for destitute chil- 

 dren. 



(a) Pure cultures. 



