524 



PATHOGENIC MICROORGANISMS 



Staining. Stained by Neisser 's or Roux's method, no polar bodies 

 can be demonstrated. The bacillus forms no spores, is non-motile, and 

 possesses no flagella. 



Cultivation. On the usual culture media B. Hoffmanni grows more 

 luxuriantly than B. diphtheriae, developing even in first isolations from 

 the human body upon the simple meat-extract media. On agar plates 

 its colonies are larger, less transparent, and whiter than are those of 



true diphtheria bacilli. In fluid media 

 there is even clouding and less ten- 

 dency to the formation of a pellicle 

 than with B. diphtheriae. A positive 

 means of distinction between the two is 

 given by the inability of B. Hoffmanni 

 to form acid upon various sugar media. 

 The differentiation on a basis of acid 

 formation was first attempted by Cob- 

 bett * and has been recently worked out 

 systematically by Knapp, 2 and con- 

 firmed by various observers. 3 The re- 

 sults of this work, carried out with the 

 serum-water media of Hiss, to which 

 various sugars were added, show that 

 B. Hoffmanni forms acid upon none of 

 the sugars used, while B. diphtheriae 

 FIG. 107. BACILLUS HOFFMANNI. acidifies and coagulates media contain- 

 ing monosaccharids and several of the 



more complex sugars, as given in the diagram in the section following, 

 dealing with B. xerosis. 



Differentiation can finally be made on the basis of animal patho- 

 genicity, B. Hoffmanni being entirely innocuous to the ordinary labora- 

 tory animals. B. Hoffmanni forms no toxins, and animals immunized 

 with it do not possess increased resistance to B. diphtheriae. 



BACILLUS XEROSIS. In 1884, Kutschert and Neisser 4 described a 

 bacillus, isolated from the eyes of patients suffering from a form of 

 chronic conjunctivitis known as xerosis. This bacillus, which, morpho- 

 logically, is almost identical with B. diphtheria?, they believed to be the 

 etiological factor of the disease. The frequency with which it has been 



1 Cobbett, Cent. f. Bakt., 1898. 2 Knapp, Jour. Med. Res., vii, 1904. 



3 Graham Smith, Jour, of Hyg., vi, 1906; Zinsser, Jour! Med. Res., xvii, 1907. 



4 Kutschert und Neisser, Deut. med. Woch., xxiv, 1884. 



