76 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



interpretations when the true form of the primary nucleus was afterwards 

 discovered, hi fact the morphology of the secondary nucleus is considerably 

 less easy, than that of the primary nucleus, to define. It consists ot a structure 

 which, although it may appear single is probably always paired and is disposed 

 centrally in the bacillus. It does not stain with the same clarity as the primary 







(Reproduo-d fnim the Journal of Hygiene.) 



Fig. 35 



THE VEGETATIVE NUCLEUS IN BACT. COLI 



Left — Primary form. 

 Right — Secondary form. 

 Acid-Giemsa < 3000. 



nucleus, so that its exact form is difficult to determine. It divides with the 

 cell, and has been observed to do so by dark-ground illununation. 



The secondarv nucleus is an alternative form which may or may not be 

 adopted in the later vegetative stages of a culture. If it is not adopted the 

 nucleus may take the form of a central, chromatinic rod, and thereafter 

 proceed to the formation of the resting nucleus, but the resting stage may also 

 be derived from the secondary nucleus. It has not been recorded as occurring 

 in spore-bearing genera, which pass directly from the primary nuclear phase 

 to the changes associated with sporulation (Chapter VI). 



The secondary nucleus was described by Piekarski as a single, spherical 

 nucleus, situated at the centre o^ the bacterium, in contrast to the primary 



