CULTIVATION OF THE BACILLUS 



401 



in fact, in some cases the diphtheritic lesion enables them to get 

 a foothold in the tissues, where 

 they exert their usual action and 

 may lead to extensive suppurative 

 change, to septic poisoning or to 

 septicaemia. In cases where a 

 gangrenous process is superadded, 

 a great variety of organisms may 

 be present, some of them being 

 anaerobic. Against such complica- 

 tions 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 : Loffler's 

 original medium (p. 41), solidified 

 blood serum, alkaline blood serum 

 (Lorrain Smith), blood agar, and the ordinary agar media. If 

 inoculations be made on the surface of blood serum with a piece 



of diphtheria membrane, 



a b 



FIG. 113. Cultures of the 

 diphtheria bacillus on au 

 agar plate ; twenty-six hours' 

 growth. (Natural size.) 

 (a) Two successive strokes ; (ft) 

 isolated colonies from the same 

 plate. 



colonies of the bacillus 

 may appear in twelve 



hours, and are well formed 

 within twenty-four hours, 

 often before any other 

 growths are visible. The 



I colonies are small circular 



discs of opaque whitish 

 R ^^^ colour, their centre being 

 thicker and of darker 

 greyish appearance when 

 viewed by transmitted 

 light than the periphery. 

 Their margins are at first 

 regular, 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 appearance 

 26 



FIG. 114. Diphtheria colonies, two days 

 old, on agar. 



x8. 



