214 CLINICAL BACTERIOLOGY. 



of interest in this connection that Roux and Yersin have 

 shown that attenuated diphtheria-bacilli can be rendered 

 again virulent by simultaneous inoculation with virulent 

 streptococci. 



Saprophytic Occurrence of Diphtheria-bacilli outside 

 the human body has not yet been observed. 



Pseudo-diphtheria-bacilli. Hoffmann Wellenhof, and 

 independently of him Loffler, cultivated as early as 1887 a 

 microorganism bearing an extraordinary resemblance to the 

 specific diphtheria-bacillus, and which Loffler designated 

 pseudo-diphtheria-bacillus. Since then, reports of obser- 

 vations of this or quite similar bacteria have multiplied, so 

 that a whole series of pseudo-diphtheria-bacilli obtained 

 from cases of angina, rhinitis, from the healthy mucous 

 membrane of the mouth, pharynx, and nose, and from the 

 skin and its diseases is now known. The confusion became 

 still greater when the xerosis-bacilli were included in this 

 group, and when it was later shown that these bacilli are 

 present upon the normal conjunctiva. 



The pseudo-diphtheria-bacillus exhibits the same varia- 

 tions in form as the true diphtheria-bacillus. The short bacil- 

 lus is said to occur more commonly, but this is by no means 

 always the case. According to M. Neisser the pseudo-diph- 

 theria-bacilli exhibit negative manifestations when double 

 staining with methylene-blue acetate and vesuvin is em- 

 ployed. Only rare examples of certain varieties of xerosis- 

 bacilli take the stain. In applying this staining reaction 

 the conditions laid down (pp. 207, 208) must be strictly 

 observed, as this means of differentiation does not suffice for 

 cultures several days old. Further, impression-preparations 

 from serum-cultures six hours old (p. 208), according to 

 Neisser, constitute a serviceable aid in differential diagnosis. 

 The pseudo-diphtheria-bacilli are not arranged in a typical 

 manner, and after the lapse of the short interval of time men- 

 tioned they do not exhibit the uniformly slender, rather long 

 form. The xerosis-bacilli develop but slightly in the course 

 of six hours ; they adhere so firmly to the nutrient medium 

 that typical accumulation does not appear in the impression- 

 preparation. The bacilli exhibit thickenings, swellings 

 in short, appear older than diphtheria-bacilli cultivated for 

 six hours upon serum usually do. In gelatin stab-cultures 

 the pseudo-diphtheria-bacilli form small colonies that spread 

 upon the surface, and after two days quickly grow larger. 



