526 



PATHOGENIC MICROORGANISMS 



a form of chronic conjunctivitis known as xerosis. This bacillus, which, 

 morphologically, is almost identical with B. diphtherise, they believed 

 to be the etiological factor of the disease. The frequency with which it 

 has been isolated from normal eyes, however, 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. diphtherise closely. It is 

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

 cal 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. 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. diphtherise. 



Differentiation. — It differs from B. diphtherise 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. The differentiations resulting may be 

 tabulated as follows: 



Hiss serum- water media plus 1% 



Dextrose 



Levulose 



Galactose 



Maimit 



Maltose 



Lactose 



Saccharose 



Dextrin 



A reference to the table shows that differentiation may be made 

 by the use of two sugars — saccharose and dextrin. B. diphtherise 

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

 charose, not from dextrin; B. Hoffmanni does not form acid from 

 either. 



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



