CHAPTER III. 

 MORPHOLOGY OF BACTERIA. 



IN shape, bacteria have the very simplest conceivable structure, 

 and although there are thousands of different kinds differing in 

 properties, they all have one of three general forms: rod-shaped, 

 spherical, or spiral. 



Bacilli. The rod-shaped organisms, which may be compared to 

 a lead pencil, are cylindrical organisms in which a longer and shorter 

 dimension may be recognized. They are the bacilli (sing, bacillus). 

 The ends of the organisms may be convex, less often flat or even 

 concave. The size also varies, some being so short that it is next 

 to impossible to tell whether they are rods or globular organisms; 

 others are comparatively long. 



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FIG. 6. The normal types of bacteria. 1-6, cocci; 7-13, bacilli; 14-16, spirilla; 

 1, micrococcus; # and 3, diplococci; 4> tetracoccus; 5, sarcina; 6, streptococcus (the 

 lower chain includes an arthrospore) ; 7 and 8, bacilli; 9, 10, IS and IS, bacilli with 

 various granules; 11, streptobacillus; 14< vibrio; 15, spirillum; 16, Spirocheta trepo- 

 nema. (Kendall.) 



Cocci. The cocci (sing, coccus) are typically spherical and may 

 be likened to a ball or at times to an egg. They may in the early 

 stages of cell division appear temporarily as bacilli with convex ends. 

 They often occur in pairs, diplococci, in which case usually their 

 proximate surfaces are flattened. This flattening of the organism 

 may at times be accompanied by an elongation of the axis of the 

 organisms parallel to the plane of opposition. This leads to the 

 coffee-bean shape exemplified in the gonococcus and miningococcus. 

 At other times we have the flattening perpendicular to the plane of 

 the flattened surface as seen in the "lance-shaped" pneumococcus. 

 The cocci may be large or small and group themselves in various 

 ways. 



