ORGANIZATION OF THE BACTERIA. 30 
observed in the long forms, the Bacillus, the Vib- 
rions, ete. As to the movement of translation, 
it is very variable; at one time slow, at another 
rapid, it is in relation with the length and form 
of the bacterium. M. Cohn has well described all 
the modifications of movement in the following 
lines : — 
“‘ Almost all the bacteria possess two different 
modes of life, characterized by repose and by 
movement. 
“In certain conditions, they are excessively 
mobile; and when they swarm in a drop of 
water, they present an attractive spectacle, sim- 
ilar to that of a swarm of gnats, or an ant-hill. 
The bacteria advance, swimming, then retreat 
without turning about, or even describe circular 
lines. At one time they advance with the ra- 
pidity of an arrow, at another, they turn upon 
themselves like a top; sometimes they remain 
motionless for a long time, and then dart off 
like a flash. The long rod-bacteria twist their 
bodies in swimming, sometimes slowly, sometimes 
with address and agility, as if they tried to force 
for themselves a passage through. obstacles. It 
is thus that the fish seeks its way through aquatic 
plants. They remain sometimes quiet, as if to re- 
pose an instant: suddenly the little rod commences 
to oscillate, and then to swim briskly backwards, 
to again throw itself forward some instants after. 
All of these movements are accompanied by a 
second movement analogous to that of a screw 
which moves in a nut. When the vibrios in the 
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