DIPHTHERIA. 289 



appearance. It must be remarked that when sudden 

 transplantations are made from blood-serum to agar- 

 agar the growth resulting is meagre, but the oftener 

 this growth is transplanted to fresh agar-agar the more 

 luxuriant it becomes. 



The growth in gelatin puncture-cultures is character- 

 ized by small spherical colonies which develop along the 

 entire length of the needle-track. The gelatin is not 

 liquefied. 



Upon the surface of gelatin plates the colonies that 

 develop do not attain anything like the size of the colo- 

 nies upon Loffler's mixture. They appear to the naked 



FIG. 79. Bacillus diphtheriae, colony twenty-four hours old upon agar-agar; 

 x 100 (Frankel and Pfeiffer). 



eye as whitish points with smooth contents and regular 

 though sometimes indented borders. Under the micro- 

 scope they appear as granular, yellowish-brown colonies 

 with irregular borders (Fig. 79). 



When planted in bouillon the organism causes a diffuse 

 cloudiness at first, but, not being motile, soon settles to 

 the bottom in the form of a rather flocculent precipitate 

 which has a tendency to cling to the sides of the glass. 

 Sometimes a delicate irregular mycoderma . forms upon 



19 



