94 MORPHOLOGY OF THE BACTERIA. 
g. Spirillum, Ehrb. 
Filament spiral, rigid; turns of spiral short 
and regular. 
S. tenue, Ehrb. 
Filament slightly tortuous, three to four turns of 
the spiral; length and diameter of a single turn, 2 to 
3 u. When the filament has a turn and a half, it re- 
sembles an 2; the filaments of two to five turns have 
a length of 4 to 15 ~; spiral movement very rapid. 
In infusions, etc. 
S. undula, Ehrb. (Vibrio prolifer, Ehrb.) 
Filament larger, turns of the spiral wider apart 
(from 3 to 5 #); having usually one half a turn to 
one full turn, rarely one and a half, two, or three; 
length 8 to 10 yp, breadth 5 yw, thickness of filament 
1.3 ~; having a very rapid spiral movement. 
Fetid animal and vegetable infusions and run- 
ning water. 
The S. rufum, Pertz only differs from this by its reddish 
color. 
S. volutans, Ehrb. 
Filament large and thick, turns of spiral regular, 
well separated, and 13 w in height; number of turns 
two, three, and three and a half, rarely six and seven ; 
total length 25 to 30 uw, thickness 1.5 w, breadth 6.6 pw; 
movement sometimes rapid, sometimes motionless ; 
a well-defined cilium, already seen by Ehrenberg 
(Cohn, Warming). 
This giant of the bacteria is found in vege- 
table and animal infusions, in sea-water, and in 
fresh water. 
