494 APPLICATION OF METHODS OF BACTERIOLOGY 



of two separate and distinct organisms that were alike in 

 cultural and morphological peculiarities, but which differed 

 in their disease-producing power. Further -studies on this 

 point have, however, shown that genuine bacillus diph- 

 therise may possess almost all grades of virulence, and that 

 absence of or diminution in virulence can hardly serve to 

 distinguish as separate species those varieties that are other- 

 wise alike; moreover, the histological conditions found at 

 the site of inoculation in animals that have not succumbed, 

 but in which only the local reaction has appeared, are in 

 most cases characterized by tissue changes that are identi- 

 cal in kind though less in degree to those seen at autopsy 

 in animals in which inoculation has proved fatal. 



In the course of their observations upon a large number 

 of cases Roux and Yersin found that it was not difficult to 

 detect, in the diphtheritic deposits of a patient ill of diph- 

 theria bacteria 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, etiologically 

 speaking, affecting only the mucous membrane of the nares, 

 known as membranous rhinitis, from which it is very com- 

 mon to obtain cultures in all respects identical with those 

 from typical diphtheria, save for their inability to kill sus- 

 ceptible animals. On inoculation these cultures produce 

 only local reactions, but these are characterized histologi- 

 cally by the same kind of tissue-changes that follow inocu- 

 lation with the fully virulent organism. 



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

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

 valescence, for this is contrary to what experience has shown to be the case. 



