232 VETERINARY BACTERIOLOGY 



brane of diphtheria, which Loffler, in 1884, secured in pure cul- 

 ture and showed to be pathogenic. A similar organism was 

 isolated by him from a healthy child, so that he was reluctant to 

 conclude that he had found the true cause of the disease. Roux 

 and Yersin, in 1888-1890, showed that the various pathologic 

 conditions most characteristic of diphtheria could be duplicated 

 in animals by injection of the broth filtrate containing the toxin. 



Distribution. Occurs in epidemics, particularly among the 

 young, in Europe and America. 



Morphology and Staining. Bacillus diphtheric? is so variable 

 in its morphology that many writers do not consider it a Bacillus 





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+ . ^ 



Fig. 98. Bacillus diphtheria (Epstein in Journal of Infectious Diseases). 



at all, but to be more closely related to some of the higher bacteria 

 or even the fungi. It stains readily with the .common anilin dyes, 

 and is gram-positive. When stained with methylene-blue a smear, 

 prepared directly from an infected mucous membrane, will show 

 rods varying from 0.4 to 1 /tf in diameter and 1.5 to 3.5 fi in length, 

 frequently slightly curved, sometimes pointed or club-shaped, 

 sometimes staining uniformly, but usually containing meta- 

 chromatic granules, which stain more deeply than the remainder 

 of the cell, and give a barred or granular appearance to the cell 

 contents. These same variations may be observed in the organism 

 taken from suitable culture-media, particularly Loffler's blood- 



