402 BACTERIOLOGY. 



toward recovery the less virulent varieties often became 

 quite frequent. 1 



There is, moreover, a mild form of diphtheria, etio- 

 logically speaking, affecting only the mucous membrane 

 of the nares, known as membranous rhinitis, from 

 w r hich it is very common to obtain cultures in all re- 

 spects identical with those from typical diphtheria, save 

 for their inability to kill susceptible animals. On inocu- 

 lation these cultures produce only local reactions, but 

 these are characterized histologically by the same kind 

 of tissue-changes that follow inoculation with the fully 

 virulent organism. 



Clinically, membranous rhinitis is never such an 

 alarming disease as is laryngeal or pharyngeal diph- 

 theria, and, as stated, the organisms causing it are often 

 of a low degree of virulence, though they are, never- 

 theless, genuine diphtheria bacteria. 



For those organisms that are in all respects identical 

 with the virulent bacillus diphtherise, save for their ina- 

 bility to kill guinea-pigs, the designation " pseudo-diph- 

 theritic bacillus " is usually employed ; but from such 

 observations as those just cited we are inclined to the 

 opinion that pmtdo-diphtheritic, as applied to an organ- 

 ism in all respects identical with the genuine bacterium, 

 except that it is not fatal to susceptible animals, is a 

 misnomer, and that it would be more nearly correct to 

 designate this organism as the attenuated or non-viru- 

 lent diphtheritic bacterium, reserving the term " pseudo- 

 diphtheritic " for that organism or group of organisms 

 (for there are probably several) that is enough like the 



1 It must not be assumed from this that the bacteria lose their viru- 

 lence entirely, or that they all become attenuated with the establish- 

 ment of convalescence, for this is contrary to what experience has 

 shown to be the case. 



