CHAPTER III. 

 BACTERIA.* 



FORM. 



FUNDAMENTAL FORM TYPES. The form of bacteria is exceedingly 

 simple. They are either spheres, straight rods, or bent rods (spiral). 

 In the spherical form they are known as cocci, or micrococci (sing, coccus 

 or micrococcus}. The straight rods are bacilli (sing, bacillus') and the 

 bent rods are spirilla (sing, spirillum'). 



ffi 



** 



,** 



v-.- **:.; 



FIG. 16. -Types of micrococci. (After Williams.) 



FIG. 17. Types of bacilli (After Williams.') 



FIG. 18 -Types of spirilla. (After Williams.) 



GRADATIONS. The difference between these fundamental form 

 types is frequently very slight. It becomes a very difficult matter, for 

 instance, to distinguish at times between the micrococcus and the bacillus. 

 There is a number of bacteria, and among them the well-known example 

 of B. prodigiosus, that are described at one time by one investigator as 



* Prepared by W. D. Frost. 



37 



