414 



DIPHTHERIA 



to septicaemia. In cases where a gangrenous process is super- 

 added, a great variety of organisms may be present, some of 



them being anaerobic. Against 

 such complications produced by 

 other organisms anti- diphtheritic 

 serum produces no favourable 

 effect. 



Cultivation. The diphtheria 

 bacillus grows best in cultures at 

 the temperature of the body; 

 growth still takes place at 22 C., 

 but ceases about 20 C. The best 

 media are the following : Lb'ffler's 

 original medium (p. 41), solidified 

 blood serum, alkaline blood serum 

 (Lorrain Smith), blood agar, and 

 the ordinary agar media. If inocu- 

 lations be made on the surface of 

 blood serum with a piece of diph- 

 theria membrane, colonies of the 

 bacillus may appear in twelve 

 " hours, and are well formed within 

 twenty-four hours, often before any 

 The colonies are small circular discs 



a b 



FIG. 117. Cultures of the 

 diphtheria bacillus on an 

 agar plate ; twenty-six hours' 

 growth. (Natural size.) 

 (a) Two successive strokes; (6) 

 isolated colonies from the same 

 plate. 



other growths are visible, 

 of opaque whitish colour, 

 their centre being thicker 

 and of darker greyish 

 appearance, when viewed 

 by transmitted light, than 

 the periphery. Their 

 margins are at first regu- 

 lar, but later they become 

 wavy or even crenated. 

 On the second or third 

 day they may reach 3 mm. 

 in size, but when numerous 

 they remain smaller. On 

 the agar media the colonies 

 have much the same ap- 

 pearance (Fig. 117) but 

 grow less quickly, and 

 sometimes they may be 

 comparatively minute, so 

 as rather to resemble those of the streptococcus pyogenes. In 



FIG. 118. Diphtheria colonies, two days 

 old, on agar. x 8. 



