CULTIVATION OF THE BACILLUS 



415 



stroke cultures the growth forms a continuous layer of the same 

 dull whitish colour, the 

 margins of which often 

 show single colonies 

 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, 

 rather thicker in the 

 middle. In none of the 

 media 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 



FIG. 119. Diphtheria bacilli from a twenty 



four hours' culture on agar. 

 Stained with methylene-blue. x 1000. 



FIG. 120. 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. 



In culture media the bacilli 



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 

 first two or three days, 

 and several days later 

 again acquires an alkaline 

 reaction. If, however, 

 the bouillon is dextrose- 

 free (p. 82) the acid re- 

 action does not occur. 

 The organism not only 

 ferments glucose, but also 

 galactose, laevulose, mal- 

 tose, and usually also 

 glycerin and lactose in 

 older cultures ; mannite 

 and saccharose are not 

 fermented (Graham- 

 Smith). 



show the same characters as in 



