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 oscillatoriaa, the spores of 

 algae 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 



