MORPHOLOGY OF BACTERIA 19 



active process of multiplication that there is considerable 

 variation in the form and size of the individual organisms. 

 The variation is explained by the fact that the form of the 

 bacterial cells at full development differs from that which 

 they possess just after or just before they have divided. As 

 the spherical organism develops preparatory to its division 

 it becomes elongated and appears as a short oval rod just 

 prior to division. A short rod becomes in the same way, at 

 the moment of its division, two organisms, the longitudinal 

 diameter of each of which may be even a trifle less than its 

 transverse diameter, when, on a superficial examination, 

 they might be mistaken for micrococci. 



Certain species of bacteria have a greater or less ten- 

 dency to remain more or less loosely attached after division 

 has taken place. This is on account of the capsule-like en- 

 velope which surrounds the organisms. This hanging to- 

 gether may cause the organisms to appear as an aggregation 

 or clump of bacteria as in the case of the staphylococcus or 

 they may be attached so closely end to end that the two or 

 more may appear almost as a single rod or filament, or again 

 as in the streptococcus the individual elements appear as a 

 chain. 



Structurally all bacterial cells belonging to the lower 

 bacteria have (1) a cell wall and (2) a cell content (cyto- 

 plasm, central body or nucleus) or, after Fischer, a proto- 

 plasmic outer layer and a central fluid. In addition to these, 

 some species have capsules, others spores, and others fla- 

 gella. Many species contain granules (metachromatic 

 bodies). Plasmolysis often causes a concentration of the 

 cytoplasm suggesting granules or spores. 



Cell wall. When bacteria are examined microscopi- 

 cally in a living condition in salt solution or bouillon, they 

 appear as colorless, refractive bodies with or without spores. 

 When staine'd preparations of these bacteria are examined, 

 they appear to have a rather indefinite cell membrane or 

 wall which surrounds a central protoplasm or cell substance. 



