54 CELL GROUPINGS 



the individual cocci most commonly appear as hemispheres 

 with the plane surfaces apposed (Fig. 43) . Sometimes they ap- 

 pear as spheres, and occasionally are even somewhat elongated. 

 The individuals in a streptococcus grouping are most com- 

 monly elongated, either in the same direction as the length 

 of the chain, or at right angles to it. The latter appearance 

 is probably due to failure to enlarge completely after division. 

 Streptococci frequently appear as chains of diplococci, that is, 

 the pair resulting from the division of a single coccus remain 

 a little closer to each other than to neighboring cells, as a 

 close inspection of Fig. 44 will show. 



If division occurs in two planes only, there may result the 

 above groupings and several others in addition. The four 

 cocci which result from a single division may remain together, 

 giving the tetracoccus or tetrad grouping. Very rarely all the 

 cocci divide evenly and the result is a regular rectangular 

 flat mass of cells, the total number of which is a multiple of 

 four. The term merismopedia (from a genus of algse which 

 grows the same way) is applied to such a grouping. If the 

 cells within a group after a few divisions do not reproduce 

 so rapidly (lack of food), as usually happens, the number of 

 cells becomes uneven or at least not necessarily a multiple 

 of four and the resultant ^a< mass has an irregular, uneven 

 outline. This grouping is termed staphylococcus (o-ra^uXos = 

 a bunch of grapes) (Fig. 46). It is the most common group- 

 ing among the cocci. 



When division occurs in all three planes, there is in addi- 

 tion to all the groupings possible to one- and two-plane divi- 

 sion a third grouping in which the cells are in solid packets, 

 multiples of eight. The name sarcina is applied to this growth 

 form (Fig. 47). The individual cells in a sarcina packet 

 never show the typical coccus form so long as they remain 

 together, but are always flattened on two or more sides. 



The above descriptions indicate how the method of divi- 

 sion may be determined. If in examining a preparation the 

 sarcina grouping appears, that shows three-plane division. 

 If there are no sarcina, but tetrads or staphylococci (rarely 

 merismopedia), then the division is in two planes. If none 

 of the foregoing is observed but only diplo- or strcpto- 



