362 



DIPHTHERIA. 



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

 coarsely granular, often nucleated and reticulated. The deep 





'i^V J/ 





n- 



^k r^' 



. .' v.. 



I / 



y 



■<-^<^ 



Fig. 122. — Diphtheria baciUi from ; 

 twenty-four hours' culture on agar. 



Stained with methylene-blue. X looo. 



is^.i 



.A , 





* . ■' / > 



X: 





J 



,t- 



Fig. 123. — Diphtheria bacilli of larger 

 size than in previous figure, showing also 

 irregular staining ot 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 

 keeping the flasks at rest a 

 distinct scum forms, and this is 

 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 



Fig. 124. — Involution forms of the diph- 

 theria bacillus ; from an agar culture of seven 

 days' growth. 



Stained with carbol-thionin-blue. x 1000. 



