178 



BACTERIOLOGY FOR NURSES 



organism in the lesion before a diagnosis of diphtheria can with 

 certainty be made. 



Morphology and Staining. The diphtheria bacillus is a slender, 

 straight or slightly curved rod ranging from 1 /* to 6 /* in length. 

 The different strains vary considerably in form and even the same 

 strain may assume a somewhat different shape under changed 

 conditions. Freshly isolated organisms often possess granules 

 which give them a beaded appearance. Others that have been 

 grown on culture media may develop swollen ends that give to 

 them the appearance of an Indian club ; others again are thicker in 



the center and taper at one or 

 both ends. When thickened 

 at one end only they appear 

 somewhat like a wedge. 

 Stained with Loeffler's meth- 

 ylene blue the bacilli may 

 appear uniformly colored or 

 they may present a barred 

 or striated appearance. The 

 round bodies in the granu- 

 lated forms (metachromatic 

 granules) stain much more 

 intensely than the rest of the 

 organism. This peculiarity 

 of form and staining appears to have a certain relation to the 

 period of growth. A twelve-hour culture is most likely to show 

 granular forms. A twenty-four-hour growth will show more club 

 forms than at twelve hours. Older cultures still stain very 

 faintly. Thus one may often see in a stained preparation the dif- 

 ferent forms side by side. The round or oval bodies which are 

 so intensely colored with methylene blue appear even more dis- 

 tinct when Neisser's stain is used. Colored by the latter method 

 the granules are almost black, while the remainder of the bacillary 

 substance is of a yellowish brown. Serum cultures of about twelve 

 hours' growth should be employed for this method. It was orig- 

 inally thought that the presence of granules in the bacilli indicated 



FIG. 27. Diphtheria Bacilli. 



