MORPHOLOGY OF BACTERIA. 75 



by a transverse constriction in the middle of the bac- 

 terial cell, which has either been very little (spherical 

 bacteria) or considerably elongated. As a rule, the 

 micro-organisms separate soon after fission, but the 

 opposite event may occur in all groups of bacteria, 

 so that, for example, chains of spheres or rods de- 

 velop. Under certain nutritive conditions the bacte- 

 riacese, vibriones, and higher bacteria give rise to the 

 production of long threads, but later these may again 

 be resolved into links. According to all recent inves- 

 tigations, division of the cell starts in the protoplas- 

 mic layer upon the wall, the central "nucleus" or 

 "cavity" is divided passively, and the cell membrane 

 takes part secondarily. This is evidently opposed to 

 the interpretation of the central body as a nucleus, 

 because division of the nucleus always precedes divi- 

 sion of the cell. 



Longitudinal growth with transverse fission is the 

 rule for the mass of bacteria, but in certain forms 

 for example, sarcina there is a regular alternation of 

 the fission in the three principal planes. At least 

 occasional division along two planes at right angles 

 to one another has been observed in very different 

 bacteria for example, in streptococci and thus cells 

 in four parts may develop, with bifurcation of the 

 chain (vide Fig. 2). 



Longitudinal division of rod forms has been ob- 

 served rarely but undoubtedly (Babes: Z. H., XX.). 

 Metschnikoff observed stellate division in a sporu- 

 lating organism known as "Pasteuria," but this can 

 hardly be classed among the bacteria in the narrower 

 sense. 



Ordinary vegetative proliferation must be distin- 



