3 6 



DIPHTHERIA. 



the growth forms a 



FIG. 91. Cultures of the 

 diphtheria bacillus on an agar 

 plate; twenty-six hours'growth. 

 (a) Two successive strokes ; (b) 

 isolated colonies from the same 

 plate. 



of toxine. Ordinary 

 bouillon becomes 

 acid during the first 

 two or three days, 

 and several days later 

 again acquires an 

 alkaline reaction. If, 

 however, the bouillon 

 is glucose-free (p. 87) 

 the acid reaction does 

 not occur. 



In these media 

 the bacilli show the 

 same characters as in 

 the membrane, but 

 the irregularity in 

 staining is more 

 marked (Figs. 92, 



continuous layer of the same dull 

 whitish colour, the margins 

 of which often show single 

 colonies partly or completely 

 separated. On gelatine at 22 

 C. a puncture culture shows a 

 line of dots along the needle 

 track, whilst at the surface a 

 small disc forms, rather thicker 

 in the middle. In none of the 

 media does any liquefaction 

 occur. In bouillon the organism 

 produces a turbidity which soon 

 settles to the bottom and forms 

 a powdery layer on the wall of 

 the vessel. By starting the 

 growth on the surface and keep- 

 ing the flasks at rest a distinct 

 scum forms, and this is speci- 

 ally suitable for the development 



FIG. 92. Diphtheria bacilli from a twenty- 

 four hours' culture on agar. 



Stained with methylene-blue. x 1000. 



