CELL GROUPINGS 



43 



sion may be determined. If in examining a preparation the 

 sarcina grouping appears, that shows three-j^lane 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 streptococci, 

 these indicate one-plane didsion only. Cocci show their 

 characteristic groupings only when grown in a liquid medium, 

 and such should always be used before deciding on the plane 

 of division. 



Fig. 49. — Staphylococcus group- 

 ing. The large flat masses are sta- 

 phylococcus grouping. Diplococcus 

 grouping, tetrads and short strep- 

 tococci are also evident. 



Fig. 50.^ Sarcina grouping. 



As the above description shows, these terms, which are 

 properly adjectives describing the cell grouping, are quite 

 generally used as nouns. Thus the terms a diplococcus, a 

 tetrad, a streptococcus, etc., are common, meaning a bac- 

 terium of the cell form and cell grouping indicated. 



Cell Form. 



Coccus — round or spherical. 



Cell Grouping. 

 diplococcus — in 2's. 

 streptococcus — in chains, 

 tetracoccus, tetrads — in 4's. 

 staphylococcus — irregular flat masses. 

 sarcina — regular, solid packets, mul- 

 tiples of 8. 



Bacillus — rod-shaped or cylindrical < , , , .,i •" V • 



\ streptobacillus — m chams. 



Spirillum — spiral-shaped. 



f diplospirillum — in 2's, little used. 



\ streptospirillum — in chains, little used 



