26 Comparative Studies 



the ground of their cultural and morphological characters. 

 He states that the lack of virulence on the part of the 

 xerosis bacillus cannot be taken as a differentiating feature, 

 because the true diphtheria bacillus is also at times non- 

 virulent. He believes the xerosis bacillus to be, as long 

 as no further point of differentiation is known, a diphtheria 

 bacillus of low virulence, and holds it to be identical with 

 the pseudo-diphtheria bacillus. 



The Massachusetts State Board of Health (26) reports 

 on some cultures isolated in the routine examination of 

 cultures taken from suspected cases of diphtheria. "Four 

 of the forty-six cultures isolated were found to be pseudo- 

 diphtheria bacilli. A few cylindrical-, pear- and hour-glass 

 shaped bacilli are occasionally seen, but involution forms 

 are not marked, even in old cultures. They are distin- 

 guished from diphtheria bacilli by being shorter, smaller, 

 more uniform in size, shape and manner of staining and, 

 as pointed out by Escherich, by a tendency to lie parallel 

 in cover-slip preparations. These bacilli are of occasional 

 occurrence, both in the throats of persons suffering from 

 non-diphtheritic throat affections and in true diphtheria 

 mingled with the Loffler bacillus. It is only in convalescent 

 cases of long duration that the pseudo-diphtheria bacilli 

 are likely to cause doubt. They might be mistaken for 

 the last few remaining diphtheria bacilli, or the reverse 

 might occur. A few remaining virulent forms may be 

 regarded as pseudo forms. Diphtheria bacilli directly 

 from the membrane of the throat or from cultures scarcely 

 developed sometimes resemble quite closely the pseudo- 

 diphtheria bacilli in morphology and staining. 



"The morphological differences are reinforced by at 

 least two biological differences of importance the absence 

 of any power to produce acids in bouillon containing 

 dextrose, and the lack of pathogenic power. 



"Though there are these three distinctive features 

 of pseudo-diphtheria bacilli characteristic morphology > 



