470 APPLICATION OF METHODS OF BACTERIOLOGY 



the virulence of which, from various causes, has been 

 modified. 



It must nevertheless be admitted that in the course of 

 microscopic examination of materials from various sources, 

 including the pharynx, one occasionally encounters micro- 

 organisms whose morphology is so like that of the genuine 

 bacterium diphtheriae as to create suspicion, and yet they 

 are at the same time sufficiently unlike it to make one cau- 

 tious in forming an opinion as to their real nature. 



Bacterium Pseudodiphtheriticum. — For a long time bac- 

 terium pseudodiphtheriticum was looked upon as being 

 entirely harmless, and the only particular in which it was 

 regarded as being of importance was in the fact that it was 

 likely to be mistaken for bacterium diphtherise. The wide 

 dissemination of this class of organisms and the demon- 

 stration of pathogenic effects in isolated instances has led 

 to the more systematic study of members of this group of 

 organisms. 



Bacterium pseudodiphtheriticum, as found under different 

 conditions, varies markedly in its morphologic and biologic 

 characters. .Some of the varieties have definite chromogenic 

 properties, producing various shades of yellow- and orange- 

 colored pigment, while others grow with a pink color. 



The occurrence of bacterium pseudodiphtheriticum, in 

 pure culture in superficial abrasions showing a slight ten- 

 dency to suppuration; the fact that these organisms, when 

 injected into the peritoneal cavity of guinea-pigs, produce 

 purulent peritonitis; that such organisms are frequently 

 encountered in vaccine virus and in the pus of vaccination 

 wounds; and that frequently in cases of mastitis in cows 

 such organisms occur in large numbers in pure culture has 

 led to the supposition that this group of organisms was 



