DIPHTHERIA. 22$ 



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. 65. Bacillus diphtherise, 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. 65). 



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 

 the surface, especially when the cultivation is made by 

 the method of Fernbach with a passing current of air. 

 This mycoderma, which may appear quite regular when 

 the flask is undisturbed, is so brittle that it at once falls 

 to pieces if the flask be moved. 



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