ORGANIZATION OF THE BACTERIA. 33 



observed in the long forms, the Bacillus, the Vib- 

 rions, etc. 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 



3 



