THE BACTERIAL NUCLEUS S5 



wliich have been observed in algx and tungi, or even in more complex 

 creatures. 



The form ot nucleus which is usually regarded as the standard equipment 

 oi" a cell, a roughly spherical, vesicular structure, is found in most bacteria 

 at some stage of their life-history, and in some at all stages. This form of 

 nucleus was not the fu-st to be described ni bacteria, nor is it the easiest to 

 demonstrate. Frequently it occurs in resting conditions of the cell, when 

 metabolic activity is low, and the nucleoprotein content, upon which " nuclear " 

 staining reactions depend, is considerably reduced. Hence, in the Bactcriacea', 

 its presence was undetected tor some years after the appearance of the active 

 nucleus, in this type oi bacterium, was well recognised. 



In those bacteria which possess spherical nuclei in the active condition it 

 is more readily demonstrable, stains clearly and apparently contains its full 

 quota of: nticlcoproteins. It is found in the active form in some, although by 

 no means all cocci, in the small cells which comprise the bacillary forms of 

 corynebacteria and mycobacteria, and in Azotohacter. In the small bacteria 

 it appears spherical and homogeneous, but in A^orohactcr, which is considerably 

 larger, it may be seen to possess a vesicular structure, consisting of an unstained 

 vacuole surrounded by chromatinic granules. It may be supposed that the 

 same structure would be found in the nuclei of the smaller cells, were it 

 possible to resolve them with the microscope. There is evidence that not all 

 these granules are cytochemically identical. 



Fig. 19 

 THE VEGETATIVE NUCLEUS 



The vegetative nucleus of bacteria appears typically in the form of paired rods, dividing 

 reductionally, and usually lying at right-angles to the long axis of the bacterium. 

 (1-4) Stained by Acid-Giemsa. 



(1) Shigella flexneri, x 5000. 



(2) Bacillus wiegaterium, x 3000. 



(3) Bacillus cereits, very slightly hydrolysed, showing the relatively small appearance of 

 the nuclei and residual basophilia in the cell envelopes. ■ 3000. 



(4) Caryophanon latiiiii, ■; 3000. 



(5) Micrococcus cvyophilus, a markedl\- multicellular Gram-positive coccus, with one 

 nuclear body in each cell. These appearances have been confused with mitotic figures by workers 



' xmaware of the septate structure of the coccus. Trichloracetic acid and Giemsa, x 5,000. 



