BACILLUS DIPHTHERIA 



525 



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 Loe filer's 

 blood serum, on agar, glycerin 

 agar, and in 'broth, its growth is 

 very similar to that of B. diph- 

 theriae, but more delicate through- 

 out. It cannot 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. diphtheriae. 



Differentiation. It differs 

 from B. diphtheria? 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 extensively confirmed 

 by others. See table on page 526. 



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- 

 theroid bacilli, largely because of their morphological resemblance to 

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

 suggested 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 no spores. It is not, at the present writing, possible to formulate 



FIG. 108. COLONIES OF BACILLUS 

 HOFFMANNI ON AGAR. 



