BACTERIUM DIPHTHERIA 469 



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. 



Clinically, membranous rhinitis is never such an alarming 

 disease as is laryngeal or pharyngeal diphtheria, and, as 

 stated, the organisms causing it are often of a low degree of 

 virulence, though they are, nevertheless, genuine diphtheria 

 bacteria. 



For those organisms that are in all respects identical with 

 the virulent bacillus diphtherias, save for their inability to 

 kill guinea-pigs, the designation "pseudodiphtheritic bacil- 

 lus" is usually employed; but from such observations as 

 those just cited we are inclined to the opinion that pseudo- 

 diphtheritic, as applied to an organism in all respects iden- 

 tical with the genuine bacterium, except that it is not fatal 

 to susceptible animals, is a misnomer, and that it would 

 be more nearly correct to designate this organism as the 

 attenuated or non-virulent diphtheritic bacterium, reserving 

 the term "pseudodiphtheritic" for that organism or group 

 of organisms (for there are probably several) that is enough 

 like the diphtheria bacterium to attract attention, but is 

 distinguishable from it by certain morphological and cultural 

 peculiarities aside from the question of virulence. 



It is a well-known fact that many pathogenic organisms — 

 conspicuous among these being bacterium pneumoniae, 

 micrococcus aureus, streptococcus pyogenes, and the group 

 of so-called "hemorrhagic septicemia" organisms — undergo 

 marked variations in their pathogenic properties; and yet 

 these organisms, when found either devoid of this peculiarity, 

 or possessing it in a diminished degree, are not designated 

 as "pseudo" forms, but simply as the organisms themselves, 



