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2. Flagella-and endospores present—Bacillus. 
Family III.—Spirillaceae. —Cells curved or spirally bent, generally 
motile through polar flagella. 
1. Cells stiff, not flexile. 
(a) Cells without flagella—Spirosoma. 
(b) Cells with one, very rarely with two polar flagella—Micro- 
spira. 
(c) Cells with a bundle of polar flagella—Spirillum. 
2. Cells flexile, spiral very close—Spirochaeta. 
Family IV.—Mycobacteriaceae. —Cells short or long cylindrical 
or clavate-cuneate in form, without a sheath surrounding the 
chains of individuals, without endospores, with true dichotomous 
branching. 
Fig. io8. —Types of spirilla. (After Williams.) 
A. In cultures possessing the characters of true bacteria. Growth 
on solid media smooth, flat, spreading. Rod with swollen ends, 
or cuneate or clavate forms—Corynebacterium. 
B. Cultures on solid media raised, folded or warty. Generally • 
short slender rods, rarely short branched. Take the tubercle stain— 
Mycobacterium. 
Family V.—Chalamydobacteriaceae. —Thread-like, composed of 
individual cells, surrounded by a sheath. Simple or with true 
branching. Ordinary vegetative growth by division in only one 
direction of space, i.e., at right angles to the longer axis. 
A. Cell contents without sulphur granules, 
i. Filaments unbranched. 
(a) Cell-division only in one direction of space, 
( b ) Cell-division in gonidial formation in three directions 
of space—Streptothrix. 
*Marine forms with cells surrounded by a very delicate 
hardly discernible sheath—Phragmidiothrix. 
