414 Diphtheria 



and a flat surrounding zone with indented edges, and a radiated 

 appearance. The colonies that develop upon Loffler's blood-serum 

 mixture are rounded, yellowish-white, good sized and more or less 

 confluent when closely approximated. They are smooth, moist and 

 shining on the surface. They are with difl&culty differentiated from' 

 those of Bacillus hofmanni, the pseudo-diphtheria bacillus. 



Gelatin. — The growth in gelatin puncture is scanty, not char- 

 acteristic, and consists of small spheric colonies along the line of 

 inoculation. The gelatin is not hquefied. 



Fig. 156. — Diphtheria bacilli (from photographs taken by Prof. E. K. Dun- 

 ham, Carnegie Laboratory, New York): a, Pseudobacillus; b, true bacillus; c, 

 pseudobacillus. 



Agar-agar. — Cultures upon the surface of agar-agar slants are 

 usually meager when contracted with those upon Lofiler's blood- 

 serum mixture, and may be whitish in color. They consist of dis- 

 crete and confluent whitish colonies devoid of differential qualities. 

 The oftener the organism is transplanted to fresh agar-agar, the 

 more luxuriant its growth becomes. The growth is rapid and lux- 

 uriant upon glycerin agar-agar. 



Bouillon. — When planted in bouillon a distinct, whitish, granular 

 pellicle forms upon the surface of the clear medium. The pellicle 

 appears quite uniform when the tube or flask is undisturbed, but it 

 is so brittle that it at once faUs to pieces if disturbed, the minute 



