518 PATHOGENIC MICROORGANISMS 



coionies which can be easily fished and again transferred to Loeffler 

 tubes or any other suitable medium. 



Diagnosis. Cultures from suspected throats are taken on Loeffler's 

 blood serum medium and incubated at 37.5 C. for 12 to 18 hours. At 

 the end of this time morphological examination by staining with Loef- 

 fler's alkaline methylene blue and by some polar body stain like that 



FIG. 106. COLONIES OF BACILLUS DIPHTHERIA ON GLYCERIN AGAR. 



of Neisser is carried out. Occasionally direct smears from the throat 

 may show the bacilli, but it is rarely possible to make a satisfactory 

 diagnosis in this way. 



Pathogenicity. Bacillus diphtherise causes a more or less specific 

 local reaction in mucous membranes, which results in the formation of 

 the so-called " pseudo-membranes." When these are characteristically 



