402 



DIPHTHERIA 



(Fig. 113) but grow less quickly, and sometimes they may be 



comparatively minute, so 

 as rather to resemble 

 those of the streptococcus 

 pyogenes. In stroke cul- 

 tures the growth forms 

 a continuous layer of the 

 same dull whitish colour, 

 the margins of which 

 often show single colon- 

 ies partly or completely 

 separated. On gelatin 

 at 22 C. a puncture 

 culture shows a line of 

 dots along the needle 

 track, whilst at the sur- 

 face a small disc forms, 



FIG. 115. Diphtheria bacilli from a twenty- ra * her thicker in the 

 four hours' culture on agar. middle. In none of the 



Stained with methylene-blue. x 1000. me di a does any liquefac- 

 tion 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. If 



the growth is started on 



the surface and the flask 



is kept at rest, a distinct 



scum forms, and this is 



especially suitable for the 



development of toxin. 



Ordinary bouillon be- ^ ^ 



comes acid during the *-. / tfc 



first two or three days, 



and several days later 



again acquires an alka- 

 line reaction. If, how- 

 ever, the bouillon is 



dextrose-free (p. 80) the FIG. 116. Diphtheria bacilli of larger size 



than in previous figure, showing also 

 irregular staining of protoplasm. From 

 a three days' agar culture. 

 Stained with weak carbol-fuchsin. x 1000. 





'"im ~ 





does not 



acid reaction 

 occur. The organism 

 not only ferments glu- 

 cose, but also galactose, 

 Isevulose, maltose, and usually also glycerine and lactose in 



