18 BACTERIOLOGICAL INTRODUCTION 



in the length, regularity, and curvature of the 

 cells. 



The principal varieties of the spirilla which are 

 named are Comma bacilli, Vibrios, and Spirochsetae. 

 The name comma bacillus was given by Koch to the 

 Cholera spirillum ; since it describes its usual shape, 

 the name has remained in common use. The comma 

 is really a segment representing a quarter turn of 

 the spiral, and, like the spiral from which it is 

 derived, varies greatly in the eccentricity of its 

 curvature. Such comma forms constitute the great 

 bulk of the organisms represented in Figs. 75, 83, and 

 86, arid in Fig. 9. 



The name Vibrio is often given to that derivative 

 of the spiral which represents a half- turn such as is 

 seen in Fig. 10 ; this may also be regarded as 

 a double comma. Occasionally in these double 

 comma forms, instead of an S-shaped organism, 

 an E-shaped form arises from a reversal of the 

 curvature. 



The term spirochseta is applied to those spirilla, 

 usually very long, in which the long axis of the 

 spiral is itself curved and undulating. 



Figs. 9 and 10 represent various forms of the 

 same spirillum. The upper figure is from a growth 

 on a solid medium, and it is in such media that the 



