Cultivation 465 



soon reach the surface of the gelatin and commence lique- 

 faction. By the second day each is about the size of a 

 pin's head, has a yellow color, and occupies the bottom of 

 a conical depression. The appearance is much like that 

 of colonies of the cholera spirillum. 



The microscope shows the colonies to be of irregular 

 shape and coarsely granular, pale yellow at the edges, 

 gradually becoming intense toward the center, and at first 

 circumscribed, but later surrounded by clear zones, resulting 

 from the liquefaction of the gelatin. These, according to 



Fig. 138. Spirillum of Denecke; gelatin puncture cultures aged forty- 

 eight and sixty hours (Shakespeare). 



the illumination, appear pale or dark. The colonies differ 

 in appearance from those of cholera in the prompt lique- 

 faction of the gelatin, their rapid growth, yellow color, 

 irregular form, and distinct lines of circumscription. 



Gelatin Punctures. In gelatin punctures the growth 

 takes place all along the track of the wire, and forms a 

 cloudy liquid which precipitates at the apex in the form of 

 a coiled mass. Upon the surface a delicate, imperfect, 

 yellowish scum forms. Liquefaction of the entire gelatin 

 generally requires about two weeks. 

 30 



