TAXONOMY 
175 
hold eight billion of them — the student commences his study of 
bacterial growths in colonies or cultures, each kind possessing 
characteristics by which they may be distinguished and differ- 
entiated. 
Tihe individuals in the colony, depending upon the kind of bac- 
teria under examination, may be globular, rod-shaped, or spiral. 
Bacteria are classed according to form into the following families 
and genera. 
Fig. 70. — Types of micrococci. ( After Williams .) 
Family I. — Coccaceae. — Cells in their free condition globular, be- 
coming but slightly elongated before division. Cell-division in one, 
two or three directions of space. 
A. Cells without Flagella. 
1. Division only in one direction of space forming an aggregation 
resembling a chain of beads — Streptococcus. 
2. Division in two directions of space forming an aggregation 
resembling a cluster of grapes — Staphylococcus. 
3. Division in three directions of space forming a package-shaped 
or cubical aggregation — Sarcina. 
B. Cells with Flagella. 
1. Division in two directions of space — Planococcus. 
2. Division in three directions of space — Planosarcina. 
Fig. 71. — Types of bacilli. ( After Williams.) 
Family II.— Bacteriaceae. — Cells longer than broad, generally two 
to six times, straight or only with an angular bend, never curved or 
