PSEUDO-DIPHTHERIA BACILLUS. 371 



there may be more than one (Fig. 125); it does not form acid 

 from glucose, is non-pathogenic 

 to the guinea-pig, and its col- 

 onies after a time tend to become 

 whiter and more opaque than 

 those of the diphtheria bacillus. 

 Involution forms may some- 

 times be produced by it. The 

 name " Hof mann's bacillus " is 

 often used to denote such an 

 organism. This organism is of 

 comparatively common occur- 

 rence : Cobbett found it 157 

 times in an examination of 692 



FIG. 125. Pseudo-diphtheria bacillus 

 persons, Ot Whom 650 Were not (Hofmann's). Young agar culture. 



suffering from diphtheria. Stained with thionin-biue. x 1000. 



Loffler, in 1887, was the^ first to describe a bacillus having closely the 

 characters of the diphtheria bacillus, but differing from it in its want of 

 virulence. He looked upon it as a distinct species, and gave it the name 

 of the pseudo-diphtheria bacillus. Hofmann, in 1888, published an account of 

 his investigations on this subject. He obtained the pseudo-diphtheria bacillus 

 from the throat in healthy conditions, and also in non-diphtheritic affections. 

 His conclusions with regard to the distinct character of this bacillus were 

 similar to those of LofBer. Since that time the organism has been the subject 

 of much research and discussion. Roux and Yersin, on the other side, found 

 a "pseudo-diphtheria" bacillus corresponding in all its characters with a 

 greatly attenuated diphtheria bacillus, and concluded that it was really of the 

 same nature. They failed to make it virulent by any method ; but this result 

 was also obtained in the case of artificially attenuated diphtheria bacilli. 

 Biggs has found that there are two varieties of pseudo-diphtheria bacilli, both 

 differing from the true diphtheria bacillus ; one of these produces an acid 

 reaction in broth containing glucose, whilst the other does not. According 

 to his statistics the two varieties appear to occur with about the same frequency, 

 and these observations have been in the main confirmed by Cobbett and 

 Phillips. Hewlett and Knight find evidence that a true diphtheria bacillus 

 may be modified so as to show the microscopic and cultural characters of the 

 pseudo-diphtheria type, this evidence being obtained both by successive exam- 

 inations of the throat after diphtheria and by modifying cultures artificially. 

 They also claimed to have in one instance transformed a bacillus of the 

 Hofmann type into a genuine diphtheria bacillus. Richmond and Salter, by 

 the passage through finches and other birds, also record successful transforma- 

 tion of a Hofmann bacillus into the true B. diphtheriae. Lesieur, in a recent 

 and exhaustive study upon the relationship existing between B. diphtheriae 

 and the so-called B. pseudo-diphthericus, records several interesting facts. 



