THE BACILLUS AND THE BACTERIOLOGY OF DIPHTHERIA 203 



4. A study of pure cultures of diphtheria and diphtheria-like bacilli 

 from sources other than those given above. 



(a) On various artificial culture media grown under various con- 

 ditions. 



(6) In living tissues of guinea-pigs, white rats, and goldfinches. 



(c) In symbiosis with other bacteria. 



The conclusions reached were as follows: Though some cultures 

 change on some of the media, each changes in its own way, and each 

 culture still has its distinct individuality. After many culture genera- 

 tions, especially when transplanted at short intervals, the different 

 varieties tend to approach each other or rather to run in lines parallel 

 with a common norm, which seems to be a medium-sized, non-seg- 

 mented bacillus producing granules in early cultures on serum and 

 growing well on all of the ordinary culture media. The non-virulent 

 morphologically typical bacilli must be classed with the virulent varieties 

 as one species, though there is little doubt that more minute study 

 would show distinct species in this group. The atypical pseudo 

 forms, however, which show no tendency to approach the norm of 

 the typical forms, must be classed as distinct species. All of the 

 pseudo and non-virulent morphologically typical varieties when inocu- 

 lated into the peritoneum of guinea-pigs in immense doses cause 

 death. Attempts have been made to give more virulence to some of 

 these varieties by successive peritoneal inoculations, but in no instance 

 has any increase of virulence or decided change in morphological or 

 cultural characteristics been noted. Two of the non-virulent, mor- 

 phologically typical varieties have also been grown in symbiosis with 

 virulent streptococci in broth for ninety culture generations trans- 

 planted every three to four days, but when separated no change in 

 virulence or other characteristics was noted. Two other varieties of 

 non-virulent morphologically typical bacilli have been inoculated into 

 goldfinches with no result. In large doses they appear to be perfectly 

 innocuous to these birds as well as do four varieties of pseudobacilli, 

 contrary to the results of Richmond and Salter. 



Since there are so many different forms or varieties of diphtheria-like 

 bacilli, it is quite possible that some of them are derived from strains of 

 the diphtheria bacillus and that under certain conditions they readily 

 regain its characteristics. This seems to be the only way to explain the 

 apparent discrepancies in the results obtained by different observers. 

 Such closely related varieties, however, do not appear to be common in 

 New York City at the present time. So we may safely say that in this 

 region at least* non-virulent diphtheria-like organisms retain their char- 

 acteristics under various artificial and natural conditions, and that they 

 may be regarded from a public health standpoint as harmless. These 

 studies seem to demonstrate that the morphologically typical diphtheria 

 bacillus is a distinct species from the atypical diphtheria-like bacilli and 

 so-called pseudo forms, and that it has many true morphological varieties 

 or sub-species which, while showing transitory ontogenic variations 

 due to change in environment and life habit, have more or less per- 



