43 2 Diphtheria 



yellowish-white or china- white color of the blood-serum cultures, 

 and are more or less distinctly divided into a small elevated center 

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

 appearance. If blood corpuscles be suspended in the agar-agar, 

 a narrow zone of hemolysis occurs about each colony. 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. 



Fig. 155. — Diphtheria bacilli (from photographs taken by Prof. E. K. Dun- 

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

 pseudobacillus. 



They are with difficulty differentiated from those of Bacillus hof- 

 manni, 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 liquefied. 



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

 usually meager when contrasted with those upon Loffler'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. 



