SPIRILLUM TYROGENUM. 365 



denser centre and peripheral zone, the space between 

 being quite clear. They are not regularly round in all 

 cases. A peculiar aromatic odor accompanies their 

 growth on gelatin. Under a low magnifying power 



\ 



Deneke's cheese spirillum, spirillum tyrogenum. From agar-agar culture 

 twenty-four hours old. 



the smallest colonies are irregularly round in outline, 

 their borders being often rough and broken, and the 

 body of the colony is frequently marked by creases or 

 ridges that give to it a lobulated appearance. The 



Colony oi spirillum tyrogenum on gelatin, twenty-four hours old. 



larger colonies under the same lens appear as granular 

 patches, a little denser at the periphery and centre than 

 at the intermediate portions. The periphery gradually 

 fades away and no distinct circumference can be made 

 out. (See Fig. 72.) The colonies of an intermediate 



