74 STUDY AND IDENTIFICATION OF BACTERIA. 



duces oedema at the site of inoculation and postdiphtheritic palsy. 

 The injection of the soluble poisons alone without the bacilli produce 

 the symptoms of the disease. 



The bacilli tend to appear as slighlty curved rods, showing varying 

 irregularities in staining, as banding or beading, and in particular the 

 presence at either end of small, deeply staining dots (metachromatic 

 granules). These are well seen with Loffler's blue, but better with 

 Neisser's method. In culture- they also show swelling at one or both 

 ends or clubbing. In secretions or in culture they show V-shapes or 

 false branching and, what is most characteristic, the parallelism four 



FIG. 27. Diphtheria bacilli involution forms. (Kotte and Wassermann.} 



or five bacilli lying side by side like palisades. Being a Gram positive 

 organism while the majority of the other pathogenic bacteria are Gram 

 negative, it is of greatest importance to stain smears by this method. 

 It is not so strongly tenacious of the gentian violet as the cocci, so 

 decolorization should not be carried too far. 



The best medium for growing it is Loffler's blood-serum. Coagu- 

 lated white of egg answers equally well, as will a hard-boiled egg the 

 shell at one end being cracked and the white cut with a sterile knife. 

 This smooth side is then inoculated and the egg placed cut side down- 

 ward in a sherry glass. If an incubator is not at hand a tube may be 

 carried next the body in a pocket. The bacillus grows better on glycerin 



