112 



CYTOLOGY 



LIFE-HISTORY OF BACTERIA 



formation of the resting nucleus, which accords very closely with those which 

 have already been described in other bacterial groups. 



The process of formation of the resting nucleus commences by the con- 

 jugation of two of the small cells produced by the fragmentation of the 

 vegetative bacillus. Their small, spherical nuclei fuse, giving rise to a typical, 

 eccentrically-staining, vesicular, resting nucleus. 



fi ® ® 



{Modified after Lindegren and Mellon.) 



Fig. 50 

 MATURATION OF THE RESTING CELL IN M. TUBERCULOSIS 



Upper line. — Sexual conjugation of cells derived from the bacillary form ; formation of 

 the vesicular nucleus. 



Lower line. — Reduction division. Two large chromosomes are formed from the vesicular 

 nucleus and one passes to each daughter cell. The vesicular nucleus is reconstituted in each ; 

 lacking the typical eccentric granule. 



Reduction follows conjugation, as in all other cases where it has been 

 described in bacteria, and resembles a mciotic cell division. The resting 

 nucleus develops a number of granular threads, which contract, forming two 

 chromosomes. The cell divides, and one chromosome passes to each daughter 

 cell. 



Beyond this stage the process ceases to resemble that which is found in 

 eubacteria. The mature cell germinates by fission, into tetrads, and thus the 

 small, elementary cells of the vegetative culture are restored (Chapter V). 



This isolated description gains greatly in force by its remarkably close 

 resemblance to the condition in most other groups, in the maturation of the 

 resting nucleus, and especially to the more recent descriptions by Morris of 

 the processes of initiation and maturation of the secondary phase in Actinomyces 

 bovis (Section G below). 



