88 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



Asexual reproduction by fission is common to most unicellular or simple 

 organisms, and is frequently found to alternate with a sexual process, as it 

 does in bacteria also. Multicellular plants and animals have short-circuited 

 this cycle, to some extent, by the production of specialised sexual cells, upon 

 which alone falls the duty of perpetuating the species. The somatic cells 

 reproduce vegetatively and asexually, but eventually die, whereas the re- 

 productive cells, after a brief vegetative career, may undergo sexual conjugation 

 and survive. In bacteria, which lack this specialisation, all cells ahke possess 

 the potential for both vegetative and sexual reproduction, although, as in 

 most other cases, few of the cells which achieve maturity in the resting stage 

 are likely to be transferred from a declining culture to a fresh medium, and 

 serve to initiate a new, vegetative generation. 



C; POST-FISSION MOVEMENTS 



(1,12,23) 



Attempts by several workers to study the mechanism of cell division in 

 living bacteria have caused an undue amount of attention to be directed 

 towards an interesting, but quite unimportant artefact, the so-called post- 

 fission movements. The phenomenon was first described by Graham-Smith 

 (1910), who perfectly understood its artificial nature. It has, however, been 

 re-examined by workers who appear to have misinterpreted its significance 

 entirely, and it has also been accorded undue prominence in many elementary 

 text-books, probably in default of more valuable information upon cell 

 division in bacteria. 



It is stated that, after division, the daughter bacteria move, with relation 

 to one another, in one of several different and characteristic ways. Smooth 

 forms slip past one another and come to lie side by side ; rough baciUi move 

 as upon a hinge at the point of division, the " snapping " movement ; and 

 others, notably coryncbactcria, perform this second movement in an exagger- 

 ated form, so that the two halves move round upon one another like the 

 closing of a pocket-knife. 



