62 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



C; THE PRIMARY I'EGETATIVE NUCEEUS 



(5, 6, 7, 9, 10, 12, 14, 27, 30, }2, 33, 3S, 43, 44, 45, 46, 4S, 50, 51, 52, 60, 61) 



In the young cultures of most cubacteria, niyxobacteria and such chlaniy do- 

 bacteria as have been described, as well as in the primary mycelium ot strepto- 

 myces, the nucleus is found in what is sometnnes described as the primary 

 form. It consists of a pair of short rod-like bodies, sometimes slightly broader 

 at the ends than the centre, lying transversely to the long axis of the bacterium, 

 and occupying almost its entire width. They are termed chromatinic bodies 

 or chromosomes, although their exact identity with tlie chromosomes of 

 plant and animal cells is dubious. They divide with the cell, splitting longi- 

 tudnially in the manner of chromosomes. In consequence of this mode of 

 division the pairs may he parallel to one another or at a shght angle. They 

 arc sometimes so close together as not to be resc»luble separately by the 

 microscope, and sometimes quite widely separated. The chromosomes were 

 originally described as single, spherical bodies, and this description is still 

 applied to their appearance in electron micrographs, and by ultra-violet light. 



Although the bodies appear rod-shaped, they show a marked tendency 

 to present the long axis of the rod to the observer, so that it has been suggested 

 that they are, in fact, disc-shaped or in the form of a short, spiral band. This 

 is to some extent supported by the observed form of the nuclei of the large 

 micro-organism Caryopluvioii liitiii}i, which resembles bacteria in many of 

 Its morphological attributes. Its nuclei are ring or disc-shaped, and lie, as a 

 rule, in a plane transverse to the long axis of the bacillus-like organism. An 

 even more remarkable demonstration of a primary vegetative nucleus m tlie 

 form of unequivocal transverse rods is given, however, by Oscillospira, another 

 member of the same group, and even larger than Caryophamvi. The con- 

 sensus of opinion is that the chromatinic bodies are, as they appear to be. 



Figs. 24 and 25 

 SECTIONS OF BACTERIAL NUCLEI 



Electron micrographs of ultra-thin sections of Bacterium coli. The material has probably 

 suffered some distortion in the process of fixation in osmium tetroxide solution and embedding 

 in synthetic resin, but nevertheless shows the absence of cross-walls in this type of bacterium, 

 and the nuclear bodies in the form of short rods in both longitudinal and transverse sections. 

 Exactly as in stained preparations, the nuclei appear singly or in pairs towards each end of 

 the cells, or in larger numbers in the filaments. 



