292 BACTERIOLOGY. 



of its virulence, and that absence of or diminution in 

 virulence can hardly serve to distinguish as separate 

 species these varieties that are otherwise alike ; more- 

 over, 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 the same changes that are seen 

 at autopsy in animals in which the inoculation has 

 proven 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 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.' 



There is, moreover, a mild form of diphtheria affecting 

 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 power to kill suscepti- 

 ble animals. On inoculation these cultures produce 

 only local reactions, but these are characterized histo- 

 logically by the same tissue changes that follow inocu- 

 lation 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. 



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

 entirely, or tb^t they all become attenuated with the establishment of con- 

 valescence. 



