Till-: HACILLUS AND THE BACTERIOLOGY OF DIPHTHERIA 199 



coccus are the two forms most frequently found in these cases, but 

 there are also others which, under suitable conditions, take an active 

 part in producing this form of inflammation. Among these is a long, 

 slender bacillus which is occasionally found in great abundance in the 

 middle layers of pseudomembranes when the diphtheria bacillus is 

 absent. This bacillus was first described by Vincent. 1 It does not 

 grow readily on artificial media and is not pathogenic in animals. 

 From its presence in the ulcerated processes and false membrane of a 

 number of cases, it is believed to have some causal relation to them. 

 This bacillus does not grow on the serum media, so that the diagnosis 

 must be made from smears. 



These cases show many of the local appearances of true diphtheria, 

 the superficial necrosis of the epithelium, the membrane of the glandu-? 

 lar swellings. The pseudomembranes may persist for from one to 

 two weeks, or even, in exceptional cases, longer. This bacillus is appar- 

 ently frequently present in the normal throat, and is probably only 

 able under certain favorable conditions, such as the influence of syphilis, 

 to produce lesions. Nerve degeneration does not follow an attack. 



The pseudomembranous angina accompanying scarlet fever, and 

 to a less extent other diseases, may not show the presence of diphtheria 

 bacilli, but only the pyogenic cocci, especially streptococci, or, more 

 rarely, some varieties of little-known bacilli. The deposit covering the 

 inflamed tissues in these non-specific cases is, it is true, usually but not 

 always, rather an exudate than a true pseudomembrane. The majority 

 of these cases, however, are mild affections, being only of importance 

 in adding to the severity of the disease which they complicate. An 

 exception should be made when the larynx is affected, as here the lungs 

 are often secondarily involved. The bacteria which occur in false 

 diphtheria are streptococci, staphylococci, diplococci, and sometimes 

 pseud odiphtheria bacilli or bacilli which are morphologically and cul- 

 turally distinct from the diphtheria bacilli. 



Persistence of Varieties of the Bacillus Diphtherias and of Diphtheria- 

 like Bacilli. The fact that there are many varieties of the diphtheria 

 and diphtheria-like bacillus has, we think, been fully established. 



But that such varieties are true sub-species with constant charac- 

 teristics, one variety not changing into another of the established forms, 

 has not been generally accepted. On the contrary, of late the idea 

 seems to be gaining ground among some investigators that all of the 

 various forms of diphtheria-like bacilli are the result of more or less 

 transitory variations of the same species, and hence that the virulent 

 forms are the result of a rapid adaptation to environment and conse- 

 quent pathogenesis of the non-virulent forms, both typical and atypical. 



This question of the relationship of the specifically virulent diph- 

 theria bacillus to non-virulent, diphtheria-like bacilli has been dis- 

 cussed since 1887. It is certainly theoretically possible that the non- 

 virulent forms have been derived from virulent forms. Whether or 



' Annales de 1'Institut Pasteur, August, 1899. 



