70 ATLAS OF BACTERIOLOGY. 



a protoplasmic body, which does not stain so readily. 

 These two structures together constitute the bacillus 

 as ordinarily conceived; they are surrounded by a 

 membrane which stains with difficulty (vide page 72). 

 According to Alfred Fischer * (Fig. 4), the condi- 

 tions are very simple and essentially different from 

 those just described. The bacterium consists of a 

 cell membrane, a protoplasmic tube, and a central 

 fluid; nothing is yet known concerning a nucleus. 



FIG. 4 a. Plasmolysis, according to A. Fischer, a, Spirillum undula; 

 6, bacterium Solmsii ; c, vibrio choleras. 



In solutions of salts (sodium chloride, potassium 

 nitrate, etc.) and the more rapidly the more con- 

 centrated the solution the abstraction of water pro- 

 duces "plasmolysis," i.e., a retraction of the proto- 

 plasmic tube with partial detachment from the cell 

 wall, f This explains numerous bright vacuoles which 

 develop in many bacilli on making an ordinary cover- 

 glass preparation, and which were formerly often 

 regarded as spores. 



At the same time and independently of A. Fischer, 

 * " Untersuchungen uber Bakterien, " 1894, Berlin. Reprint 

 from the Jahrb. f. wiss. Botanik, xxvii., vol. 1. 



f Desiccation on the cover-glass often suffices to produce pic- 

 tures of plasmolysis. 



