FORM AND STRUCTURE OF BACTERIA 19 



anthracis. The motile spore-producing forms are called bacilli 

 by Migula, as noted above. Not infrequently are bacilli 

 surrounded by gelatinous capsules, e.g. B. capsulatus. It is 

 quite common for some bacilli to grow in chains and form 

 long threads under certain conditions, e.g. Bact. anthracis, or 

 B. subtilus in beef broth (Figs. 10, n). On careful examina- 

 tion it will be seen that the long threads or filaments are made 

 up of individual bacteria, although at first sight the thread 

 may appear to be homogeneous throughout. 



Spirilla. Besides the cocci and bacilli there is one other 

 common group of lower bacteria known as the spirilla. These 

 bacteria, as their name indicates, are spiral or corkscrew 

 shaped. They are composed of rods, not unlike bacilli, but 

 in addition they are twisted so as to make them appear as 

 spirals. The spiral may be a short, one fourth turn or less 

 (Microspira comma) (Fig. 12), 



or may be long and possess * / 



seveqral turns (Spirillum ru- 9 f^ 



brum). The name microspira c, , 



or vibrio has been applied to { \ 2, 



those spirilla which are very ^ 



short, and make but a fraction ^^ 



^^f ^f\ ^f^S* 



of a turn. The Mkrospira fci f\ { 

 comma of Asiatic cholera is FIG. ^.-Microspira comma. After 

 frequently called the Vibrio of Schmidt and Weis - 



Asiatic cholera. Koch called this last-mentioned organism the 

 " Comma bacillus," on account of its resemblance to a print- 



