THE BACTERIAL NUCLEUS 59 



Coccal genera which possess this type e>f nucleus may often form short 

 filaments ccMitaining hnir or five nuclei. These filaments are entirely distinct 

 from the reproductive filaments formed by many bacteria, including strepto- 

 cocci, which possess nuclei of the chromosomal type (Sections C and D below). 



Where the spherical nucleus is found only ni the resting stages of the 

 bacterium it is often more obviously vesicular and stains eccentrically. The 

 main body of the nucleus stains poorly or not at all, and may be difficult to 

 distinguish from the cytoplasm of the cell. The stainable portion of the 

 resting nucleus is sometimes merely a crescentic portion of the outline, but 

 may take the form of a single or double spherical body at one edge. Often 

 this is the only portion of the nucleus which can be resolved, and the 

 appearance is of a small, double, spherical nucleus lying eccentrically in the 

 cell. In the case of myxobacteria and cytophagas the stainable portion may 

 be tadpole-shaped. 



The spore nucleus resembles other resting nuclei, but appears to be in a 

 condition of turgour (possibly due to concentration of the protein materials, 

 Chapter IX). The effect of acid-hydrolysis is to weaken the spore-coat, so 

 that the nuclear material may be forced from its natural position to lodge as 

 a pool of basophilic material at the periphery of the cell. The appearances 



THE SPORE NUCLEUS 



The bacterial endospore has a vesicular resting nucleus, typical of such nuclei, except 

 that it appears to be in a condition of turgour when mature. Under the influence of acid- 

 hydrolysis processes the nuclear material may be partly or completely ejected, giving the 

 various appearances which have, in the past, been described as " peripheral " or " crescentic " 

 nuclei. The immature spore nucleus does not behave in this fashion. The weak spot, through 

 which the nuclear material may be ejected, possibly represents a germination pore. 



(1) Spores of Bacillus sp., treated with N/1 nitric acid for 5 minutes, stained Giemsa and 

 re-stained tannic-acid-violet, to demonstrate that the ejected nuclear material is outside the 

 spore coat. One spore has retained it within the spore coat and shows the " peripheral 

 nucleus." -5000. 



(2) Spores of B. siibtiHs. showing the spore nucleus in its natural condition. Acid-Giemsa. 

 X 3000. 



(3, 4) Spores of Clostridium u\=lchii. Nitric acid for 10 minutes, stained crystal violet. 

 All types of appearances seen ; a, nucleus in natural condition ; b, " crescentic nucleus " ; 

 £, " peripheral nucleus." Other sporeg are in intermediate stages, x 3000. 



(5) Maturing spores of CI. welchii, as in (3, 4), showing no change of position of nucleus. 



(6) As (1), after several hours hydrolysis. 



(7) As (I), electron micrograph, gold-shadowed. ,-, 16,000. 



