334 Wisconsin State Hoeticultural Socibty. 



single little rod in twenty-four hours ; but at the end of the fol- 

 lowing day the bacteria would fill a space equal to 442,570 such 

 cubes. Take the space which is occupied by the seas of this 

 world, about two-thirds of the terrestial surface, say with a mean 

 depth of -a mile, the collective contents of which would be nine 

 hundred and twenty-nine millions of cubic miles ; by continual 

 progression of multiplication the bacteria which spring from one 

 germ would in less than five days fill the whole world's seas com- 

 pletely full; the number can only be expressed by figures of 

 thirty-seven places. 



" Almost all bacteria," Professor Cohn states, " have two dif- 

 ferent modes of life, one characterized by repose, and one by 

 motion. In certain conditions they are excessively mobile, and^ 

 when they swarm in a drop of water, they present an attractive 

 spectacle, similar 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 rapidity of an arrow, at another they turn upon themselves 

 like a top ; sometimes they remain motionless for a long time, 

 and then dart ofi 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 repose an 

 instant ; suddenly the little rod commences to oscillate, and then 

 to swim briskly backward, to again throw itself forward some in- 

 stants after. All of these movements are accompanied by a sec- 

 ond movement analogous to that of a screw which moves in a 

 nut. When the vibrios, in the 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." 



Efforts have been made to account for these movements in va- 

 rious ways. An explanation, given by some, is that they are the 

 voluntary movements of real animal life ; others reply that the 

 same motions are seen in forms of life known to be vegetable. 

 Another theory is that the motion is produced by arms or cilia 



