THE LIFE HISTORY OF BACTERIA. 45 



eventually yields a long row or chain of attached micro- 

 cocci. This exceedingly characteristic form is known as a 

 streptococcus, and as indicated, its formation is analogous to 

 that of a thread. It may be compared to the beads on a 

 rosary (Fig. 10 &). 



In the above instances the dividing membrane always 

 forms in a plane parallel to the original plane of division.- 

 Consequently growth extends, as it were, along a line. The 

 division is then said to occur in one direction of space. 

 This does not hold true for all micrococci. Thus, after the 

 original cell divides into two, each of these in turn may 

 divide so that the line of division is at right angles to that 

 in the original cell. The four cells which thus result are 

 not arranged in a row, but form a tetrad, which may be com- 

 pared, when stained, to the four spots on a die. Division 

 has been consecutive and in two directions of space (Fig. 

 10 c; also Fig. 5 &). 



Again, each of the four cells of a tetrad may divide so 

 that the plane of division will be parallel to the face of the 

 tetrad. The result is a cubical mass of eight cells. This 

 package-shaped mass of micrococci is known as a sarcine. 

 Division has been consecutive and in three directions of 

 space (Fig. 10 d). 



Lastly, micrococci may divide rather irregularly and, 

 remaining adherent, eventually yield a mass of cells which 

 resemble somewhat a bunch of grapes. Such forms are 

 designated as staphylococci (Fig. 10 e). 



Whatever may be the final form which results from the 

 division of micrococci, whether the division occurs in one, 

 two or three directions of space, it is always to be under- 

 stood as consecutive. That is to say, one cell divides into 

 two; these two, on division, yield four cells, and the latter 

 in turn yield eight cells. One micrococcus never divides 

 directly into quarters or into eighths. 



The simple micrococcus, as shown above, may multiply 

 so that it usually appears as a single cell. When the cells 



