584 PATHOGENIC MICROORGANISMS 



tory animals. B. Hoffmann! forms no toxins, and animals immunized 

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



BACILLUS XEROSIS. In 1884, Kutschert and Neisser 47 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. diphtheriae, they believed to be the 

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

 isolated from normal eyes, precludes this etiological relationship, and 

 it may safely be regarded as a harmless parasite which may indeed be 

 more abundant in the slightly inflamed than in the normal conjunctiva. 

 Morphology. B. xerosis resembles B. diphtherias closely. It is 

 occasionally shorter than this, but on the whole no absolute morpho- 

 logical differentiation between the 

 two is possible. It forms no spores 

 and is non-motile. Polar bodies may 

 occasionally be seen. 



Cultivation ' On Loeffler's blood 

 serum, on agar, glycerin agar, and in 

 broth, its growth is very similar to 

 that of B - diphtheriae, but more del- 

 i ca te throughout. It cannot easily 

 be cultivated upon the simple meat- 

 FIG. 63. BACILLUS XEROSIS. extract media, nor will it grow on 



gelatin at room temperature. Its 



colonies on glycerin or glucose agar are microscopically identical with 

 those of B. diphtheriae. 



Differentiation. It differs from B. diphtheriae distinctly in its acidi- 

 fying action on sugar media. These relations were first worked out by 

 Knapp for various sugars and the alcohol mannit, and have been exten- 

 sively confirmed by others. See table on page 585. 



A reference to the table shows that differentiation may be made 

 by the use of two sugars saccharose and dextrin. B. diphtheriae 

 forms acid from dextrin, not from saccharose; B. xerosis from saccha- 

 rose, not from dextrin; B. Hoffmanni does not form acid from either. 

 B. xerosis is non-pathogenic to animals and forms no toxin. 

 The Diphtheroid Bacilli. In addition to the bacteria mentioned 

 above, there is a large group of microorganisms spoken of as the diph- 

 iheroid bacilli, largely because of their morphological resemblance to 

 the diphtheria bacillus. For this group, Lehman and Neumann have 



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



