CULTIVATION OF B. DIPHTHERIA. 



361 



sive swelling of the tissues of the neck, sometimes attended by 

 suppuration in the glands, and also various haemorrhagic con- 

 ditions, have been found to be associated with their presence ; 

 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 super- 

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

 them being anaerobic. 



Against such complications anti-diphtheritic serum produces 

 no favourable effect, as its action is specific and only neutralises 

 the toxins of the diphtheria bacillus. In view of this fact, in 

 some cases the anti-streptococcic serum has been used along with 

 it, and it is apparent that in such conditions the bacteriological 

 examination of the parts affected may afford valuable indications 

 as to treatment. 



Cultivation. The diphtheria bacillus grows best in cultures 

 at the temperature of the body ; growth still takes place at 22 

 C., but ceases at 20 C. The best 

 media are the following : Lb'ffler's 

 original medium (p. 45), solidified 

 blood serum, alkaline blood serum 

 (Lorrain Smith), blood agar, and 

 the ordinary agar media. If in- 

 oculations be made on the surface 

 of blood serum with a piece of 

 diphtheria membrane, colonies of 

 the bacillus appear within twenty- 

 four hours, and often before any 

 other growths are visible. The 

 colonies are small circular discs 

 of opaque, whitish colour, their 

 centre being thicker and of darker 

 greyish appearance when viewed by transmitted light than the 

 periphery. On the second or third day they may reach 3 mm. 

 in size, but when numerous they remain smaller. Upon agar 

 plates the surface colonies at the end of twenty-four to forty- >' 

 eight hours' incubation resemble those of streptococcus pyogenes, 

 but are usually larger and have a tendency towards wavy mar- 

 gins. Under the low power of the microscope such colonies 



a b 



FIG. 121. Cultures of the diph- 

 theria bacillus on an agar plate; twenty- 

 six hours' growth. 



(a) Two successive strokes; 



(b) isolated colonies from the same plate. 



