404 



DIPHTHERIA 



Fig. 



114. — Diphtheria bacilli from a twenty- 

 four hours' culture on agar. 

 Stained with methylene-blue. x 1000. 



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 flask is kept at 

 rest, a distinct scum 

 forms, and this is especi- 

 ally 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. 79) the 



acid reaction does not 



occur. 



It would be a great ad- 

 vantage if virulent diplith eiia 

 bacilli could always be dis- 

 tinguished by their growth 

 characters and fermentation 

 reactions, but unfortunately 

 this is not the case. Accord- 

 ing to Graham-Smith the 

 diphtheria bacillus ferments 

 not only glucose, but also 

 galactose, laevulose, maltose, 

 dextrin, and usually also 

 glycerin and lactose in older 

 cultures ; mannite and sac- 

 charose are not fermented. 

 Of these reactions Hine con- 

 siders that fermentation of 

 glucose and dextrin and non- 

 fermentation of saccharose indicate a true diphtheria bacillus. But, on 

 the one hand, u virulent organisms may conform with these reactions 



Fig. 115. — Diphtheria bacilli of larger size 



than in previous figure, showing also 



irregular staining of protoplasm. From 



a three days' agar culture. 



Stained with weak earbol-fuchsm. x 1000. 



