REPRODUCTION OF BACTERIA BY FISSION 



17 



the filaments of the trichobacteria cell-division means growth and increase 

 of length of the filament, and the process can only be called multiplication 

 when a cell detaches itself from its fellows and grows out into a new 

 filament. Among the unicellular haplobacteria, however, each cell-division 

 means duplication of the individual. The procedure follows the same course 

 as it does in the tissues of the higher plants. The cell first increases in 

 length, and then becomes divided into two by a transverse wall. The 

 spherical bacteria (cocci) assume an ellipsoidal figure before dividing, and 

 the two new cells are at .first flattened where they are in contact, rounding 

 off to perfect spheres again as they separate. Of the finer details of the 

 process nothing has been seen among 

 the bacteria, nor anything resembling 

 those changes in the arrangement of 

 the cell-contents which characterize 

 cell-division in the higher organisms. 

 The protoplasm is simply abstricted 

 into two parts separated by the in- 

 growing cell-wall, as in Cladophora. 

 In the filaments of this alga cell- 

 division is ushered in by the deposi- 

 tion of a ring of cellulose on the 

 inner surface of the cell-wall, where 

 the new partition is to arise (Fig. 9, a). 

 By constant addition to its inner 

 edge this ring grows broader, until 

 at last, cutting through the proto- 

 plasm, it stretches right across the 

 lumen of the cell and divides it into 

 two equal parts. There seems little 

 doubt that division of the bacterial cell takes place in the same way, but 

 the details of the process are too minute even for our best microscopes to 

 follow. 



Under the most favourable conditions of temperature and nutrition cell- 

 division takes place in a very short time. B. subtilis, the ' hay-bacillus,' 

 completes the process in half an hour. The cholera vibrio needs only 

 twenty minutes, so that in one day a single ' comma-bacillus ' would rejoice 

 in a progeny of sixteen hundred trillions. This mass of bacteria would 

 contain one hundred tons of solid residue, and it would thus be necessary 

 to make experiments on a gigantic scale to allow even one single cell to 

 multiply with perfect freedom. In nature, of course, this increase in 

 geometrical progression can never take place : in the first place, because the 

 necessary supply of food is never present, not even in the diseased body, and 

 then again because many of the bacteria soon perish, and the accumulation 



FIG. 9. Transverse division of a multinuclear living; 

 cell of an alga {Cladophora fracta). The new celt 

 wall (as in all multinuclear cells) arises independently 

 of the division of the nuclei. In Fig. a the new trans- 

 verse cell-membrane grows out as a ring at right 

 angles to the sides of the cell and appears (in optical 

 section) as rod-like outgrowths from the latter, the 

 free ends being surrounded by granular protoplasm. 

 The large round bodies are starch grains. Fig. b 

 represents an older stage, the new membrane is com- 

 plete with the exception of a small spot in the centre. 

 The figure is meant to give an idea of what probably 

 takes place during the fission of bacteria which are 

 too minute to allow the process to be followed. From 

 Strasburger. Magn. 600. 



