526 



PATHOGENIC MICROORGANISMS 



Marphologj,.-*. xerosis resembles B. diphtheria closely. It is 

 occasionally shorter than this, but on the whole no abso- 

 lute morphological differentiation between the two is possi 

 forms no spores and is non-motile. Polar bodies may occasionally 



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k. 



Cultivation. On Loeffler's blood serum, on agar, glycerin agar, and 

 in broth, its growth is very similar to that of B. diphtherias, but more 



delicate throughout. It can 

 not easily be cultivated upon 

 the simple meat-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. diphtherias. 



Differentiation. It differs 

 from B. diphtherias distinctly 

 in its acidifying 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 showing differentia- 

 tions on page 527. 



A reference to the table 

 shows that differentiation may 

 be made by the use of two 

 sugars saccharose and dex- 

 trin. B. diphtherias forms acid 



from dextrin, not from saccharose; B. xerosis from saccharose, 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- 

 theroid bacilli, largely because of their morphological resemblance to the 

 diphtheria bacillus. For this group, Lehman and Neumann have sug- 

 gested the term corynebacterium. The characteristics of this group are 

 a morphological similarity to the diphtheria bacillus, that they are 

 Gram-positive, non-motile, often show metachromatic granules and have 



FIG. 109 BACILLUS XEROSIS. 



