34 MORPHOLOGY OF THE BACTERIA. 
shape of a gimlet turn rapidly round their axis, 
they produce a singular illusion: one would be- 
lieve that they twisted like an eel, although they 
are extremely rigid.” 
The causes of these movements have been sought, 
at first, in the supposed animal nature of the bac- 
teria, and the movements assimilated, consequently, 
to voluntary movements ; but this opinion can no 
longer be sustained, as similar movements are to 
be seen in a great number of vegetable organisms, 
such as the diatoms, the oscillatoriz, the spores of 
aleve and some fungi, etc. They have also been 
attributed to the existence of locomotor appen- 
dices (Ehrenberg); but, although the cilia, denied 
at first by most microscopists, have been seen since 
in nearly all the bacteria, the botanists who have 
best studied them, M. Warming, for example, rec- 
ognize that it is scarcely probable that these or- 
gans are the cause of their movements, for “ one 
meets some examples in which the body remains 
motionless while the cilia are in violent agitation, 
and others in which the body moves while the cilia 
remain inert, or dragging behind.” 
The movements appear to depend rather upon 
the nutrition, or respiration, and especially upon 
the presence of oxygen.(Cohn); indeed when this 
gas is wanting the bacteria become motionless. 
Immobility may also be produced by want of 
nutriment, poisoning by different toxic substances, 
(chloroform, iodine, etc.), dessication, etc. 
The attempt has been made to use the charac- 
ters derived from the existence or absence of 
