REPRODUCTION OF BACTERIA 13 



Bacteria. Reproduction by transverse fission is common 

 to all bacteria ; the bacterial cell becomes constricted at 

 its middle and finally separates into two parts, and thus 

 two young cells take the place of the parent one ; repro- 

 duction by fission is therefore also an increase in numbers. 

 The fission is always transverse, never longitudinal, 1 the 

 rule being in cell-division that the new membrane is 

 formed in the most economical manner. Longitudinal 

 division, on the other hand, is comparatively common 

 among the Protozoa. Previous to division the rod-forms 

 become elongated and the spherical ones ellipsoidal, and 

 there is an increase in the number of the roseine-staining 

 granules, partly by division of pre-existing ones and partly 

 by new formation. The constriction in the majority of 

 cases involves and passes through one of the granules. 

 In the monotrichous and lophotrichous bacteria it is 

 always the non-flagellated end of the dividing cell which 

 bears the flagella of the new cell. Under favourable 

 conditions reproduction may be very rapid, fission occurring 

 every twenty or thirty minutes (Klein), so that, the increase 

 being in a geometrical ratio, the number of individuals 

 which might arise from a single bacterium in three or four 

 days is almost inconceivable, and would en masse weigh 

 thousands of tons ; fortunately there are many checks to 

 such a rapid multiplication. Frequently, although the 

 protoplasm divides, the division of the cell-membrane is 

 incomplete, resulting in a loose union of the cells with the 

 formation of a pseudo-filament. These filaments often 

 become much curved and twisted, forming tangled masses, 

 owing to fission taking place in the cells in the middle of 

 the filament as well as at the ends, so that the filaments 

 have to become curved to make room for the new cells. 



1 Longitudinal division has been described in a few species, but its 

 occurrence is so rare that a doubt must arise as to whether these forms 

 are true bacteria. 



