24 



OUTLINES OF BACTERIOLOGY 



place. This is seen in Fig. 37a, in which each cell has two division- 

 walls. In this particular case it is evident that each cell is destined to 

 become a four-celled group (Tetracoccus). The further development 

 of each of these is represented in Fig 37&, e, d t e; expansion and con- 

 striction take place till we have the stage represented in b, then the 



cell-group may thicken its new walls to 

 form the stage shown by e, after which 

 its development is complete. It may, 

 however, proceed further by splitting up 

 as represented in d, in which the four 

 cells are separated by a thin mucilaginous 

 cross. In e the separate cells round them- 

 selves off, complete the thickening of the 

 walls, and then separate, becoming one- 

 celled individuals (Unicocci). The forma- 

 tion of two-celled individuals (Diplococci) 

 takes place by a further development of 

 the e stage, in which only one of the inner 

 cross-walls forms a separating mucilaginous 

 line. The stages are shown in Fig. 37/ 5 g. 

 A three-celled individual (Tricoccus) is 

 formed from the Diplococcus by the further 

 division of only one of the cells. 



In healthy cultures, the cell-groups very 

 often consist almost entirely of mono-, diplo-, tri-, and tetracocci : 

 under somewhat different conditions, the cocci do not separate as 

 soon as formed, but remain attached, and 

 undergo further division. The result of this 

 is that packets of cocci, resembling bales of 

 cotton (Fig. 38) are formed. Many of the 

 cocci composing these packets have division- 

 walls, the division in these having gone no 

 further than the formation of walls. When 

 some of the large bales are moving slowly, it 

 can be seen that in many of them division-walls 

 are found in three directions of space, that is 

 to say, a coccus is divided into octants, and 

 each wall is at right angles to the other two. 

 division takes place in three directions of space, 



With regard to the formation of micrococci, i.e. cocci which divide 

 only in two directions of space, producing a plate of cells, it will be 



FIG. 37. Cell-division in round- 

 cells. (For explanation see text.) 



FIG. 38. Cocci united to 

 form packets. 



This shows that 



