CLASSIFICATION OF BACTERIA IN FAMILIES. 53 



The bacilli comprise all oval or rod-formed bacteria. 

 (See Fig. 3.) 



To the spirilla belong all organisms that are curved 

 when seen in short segments, or when in longer threads 

 are twisted in the form of a corkscrew. (See Fig. 4.) 



FIG. 3. 



d e f 



a. Bacilli in pairs. 6. Single bacilli, eand d. Bacilli in threads. 



e and /. Bacilli of variable morphology. 



FIG. 4. 



/;** 



tS \^f 



a b c 



a and d. Spirilla in short segments and longer threads the so-called comma 

 forms and spirals, b. The forms known as spirochseta. c. The thick spirals 

 sometimes known as vibrios. 



The micrococci are subdivided according to their pre- 

 vailing mode of grouping, as seen in growing cultures, 

 into staphylococci those growing in masses like clusters 

 of grapes (see Fig. 2, a) streptococci those growing in 

 chains consisting of a number of individuals strung 

 together like beads upon a string (see Fig. 2, b) ; diplo- 

 cocci those growing in pairs (Fig. 2, c) ; tetrads those 



