86 STUDY AND IDENTIFICATION OF BACTERIA 



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

 granules). These granules may be seen in an eighteen-hour culture, 

 but within thirty-six hours, may be abundant. 



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



FIG. 26. Bacillus of diphtheria. (X 1000.) (Williams.) 



positive organism while the majority of the other pathogenic bacilli 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. 



An egg medium, made of the whole egg with glucose bouillon as described pre- 

 viously, is as suitable as Loffler's serum. Coagulated white of egg answers fairly 

 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 downward 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 glycerine agar than on 

 plain agar. On such plates they appear as small, coarsely granular colonies with a 

 central dark area. In size the colonies resemble the streptococcus. On blood- 

 serum the colonies are larger 1/12 to 1/8 inch in diameter. 



The diphtheria bacillus grows luxuriantly on blood agar and like the streptococcus 

 pyogenes has a yellowish laked zone around the colony. The Hofman and the 

 Xerosis bacillus do not seem to have this haemolytic power. In bouillon it tends 



