50 



CELL FORMS 



The third cell form is the spiral, typified by a section of a 

 cork-screw and named spirillum, plural spirilla (Fig. 36) . A 

 very short spiral consisting of only a portion of a turn is some- 

 times called vibrio (Fig. 37). Vibrios when seen under the 



Fig. 32.— Cocci. 



Fig. 33.— Bacilli. 



microscope look like short curved rods. The distinction 

 between the two can be made only by examining the organ- 

 ism alive »r:(\ Tnnvins; in a liquid. The vibrio shows a char- 

 actensuc smrai iwistmg motion. Very long flexible spirals are 



Fig. 34.— Short bacilli. 



Fig. 35. — Curved bacilli. Only 

 the one in the center of the field is 

 in focus. The others curve out of 

 focus. 



usually named spirochetes (Fig. 38). The spirochetes are 

 motile but flagella have not been shown to be present. 



Besides the three typical cell forms bacteria frequently 

 show very great irregularities in shape. They may be 



