OUTLINES OF BACTERIOLOGY 



new cells that are formed do not always separate, but usually remain 

 attached. When two cocci are bound together the combination is 

 called a Diplococcus (Fig. 3a), if they are four in number and arranged 

 in a square, we call them a Tetracoccus (Fig. 31). More rarely may be 

 found a plate of three cocci arranged in the form of a triangle. This 

 is called a Tricoccus (Fig. 3c). Sometimes division takes place in all 



three directions of space, so that 

 there is formed a mass of cocci 

 clinging together. 



The term Packet Form is applied 

 to this mass, if the individuals 

 are regularly arranged (Fig. 4a). 

 If, however, the cocci are irregu- 

 larly arranged, resembling, for 

 example, a bunch of grapes, the 

 term Staphylococcus is applied to 

 the group (Fig. 4&). 



Finally the division may take 

 place in one direction only, so 

 that the cocci arrange themselves 

 to form a chain. This is called 

 the Chain Form (Fig. 4d). These 

 various methods of combination 

 enable us to subdivide the cocci- 

 species of bacteria into classes, because it has been found that some 

 species divide, for example, to form chains, and never in any other 

 way. A classification of the cocci forms, based on these facts, has 

 therefore been drawn up as follows : 



I. Streptococcus. Those which divide to form a chain of cocci 

 (Fig. 4d). 



II. Micrococcus.) The species belonging to these two groups divide 



III. Planococcus. J always in the same two planes, so that a plate 

 of cocci is formed. They may form diplococci, tricocci or tetracocci, 

 or even groups of more than four (Fig. 4c), but they never divide in 

 three directions of space. The name Micrococcus has been applied to 

 each of the species of this description which is non-motile, whereas the 

 name Planococcus is given to each of the motile species. 



IV. Sarcina. ^ These two groups differ from II. and III. in 

 V. Planosarcina. / that, in addition to showing the methods of 



combining together followed by the latter, they are also able to divide 

 in all three directions of space, i.e. they have the power of forming 



FIG. 4. 



