PATHOGENIC PEOPEETIES. 339 



In the course of their observations upon a large num- 

 ber of cases Roux and Yersin found that it was not 

 difficult to detect, in the diphtheritic deposits of one and 

 the same individual, bacilli of identical cultural and 

 morphological peculiarities, but of very different degrees 

 of virulence, and that with the progress of the disease 

 toward recovery the less virulent varieties often became 

 quite frequent. 1 



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

 ing only the mucous membrane of the nares, known as 

 membranous rhinitis, from which it is very common to 

 obtain cultures in all respects identical with those from 

 typical diphtheria, save for their inability to kill suscep- 

 tible animals. On inoculation these cultures produce 

 only local reactions, but they are characterized histolog- 

 ically by the same 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 bacilli. 



For those organisms that are in all respects identical 

 with the virulent bacillus diphtherice, 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 ^sewrfo-diphtheritic, as applied to an organ- 

 ism in all respects identical with the genuine bacillus, 

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



1 It must not be assumed from this that the bacilli lose their virulence 

 entirely, or that they all become attenuated with the establishment of con- 

 valescence. 



