400 BACTERIOLOGY. 



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. 



Fig. 78. 



I 



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

 twenty-four hours old. 



Under low magnifying power the smallest colonies are 

 irregularly round in outline, their borders being often 

 rough and broken, and the body of the colony is fre- 

 quently marked by creases or ridges that give to it a 

 lobulated appearance. The larger colonies under the 



Fig. 79. 





&' 



% 



X-. ' ;■■> >" 



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



same lens appear as granular patches, a little denser at 

 the periphery and centre than at the intermediate por- 

 tions. The periphery gradually fades away and no dis- 

 tinct circumference can be made out. (See Fig. 79.) 

 The colonies of an intermediate size, about which lique- 



