The above descriptions indicate how the method of division 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 streptococci, these indicate one-plane division 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. 47.—Staphylococcus grouping. The large flat masses are staphylococcus grouping. Diplococcus grouping, tetrads and short streptococci are also evident.
Fig. 48.—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 bacterium of the cell form and cell grouping indicated.
| Cell Form. | Cell Grouping. |
|---|---|
| coccus—round or spherical. | diplococcus—in 2’s. streptoccus—in chains. tetracoccus, tetrads—in 4’s. staphylococcus—irregular flat masses. sarcina—regular, solid packets, multiples of 8. |
| bacillus—rod-shaped or cylindrical. | diplobacillus—in 2’s. streptobacillus—in chains. |
| spirillum—spiral-shaped. | diplospirillum—in 2’s, little used. streptospirillum—in chains, little used. |
- diplococcus—in 2’s.
- streptoccus—in chains.
- tetracoccus, tetrads—in 4’s.
- staphylococcus—irregular
- flat masses.
- sarcina—regular, solid packets, multiples of 8.
- diplobacillus—in 2’s.
- streptobacillus—in chains.
- diplospirillum—in 2’s, little used.
- streptospirillum—in chains, little used.