362 DIPHTHERIA. 



are found to be of a grey-yellow colour, translucent, rather 

 coarsely granular, often nucleated and reticulated. The deep 





** 





FIG. 122. Diphtheria bacilli from a FlG. 123. Diphtheria bacilli of larger 



twenty-four hours' culture on agar. size than in previous figure, showing also 



Stained with methylene-blue. X 1000. irregular staining of protoplasm. From a 



three days' agar culture. 



Stain : weak carbol-fuchsin. X 1000. 



colonies show nothing very striking. In stroke-cultures the 

 growth forms a continuous layer of the same dull whitish colour, 

 the margins of which often show single colonies partly or com- 



pletely separated. On gelatin 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 



rlG. 124. Involution forms of the diph- 

 theria bacillus ; from an agar culture of seven keeping the flasks at rest a 



carboMhionin-b.u, x ,000. f S - 



especially suitable for the de- 



velopment of toxin. Ordinary bouillon becomes acid during 

 the first two or three days, and several days later again acquires 



