MORPHOLOGY, REPRODUCTION, ETC. 23 



The carbohydrates isolated from various bacteria consist chiefly of 

 small quantities of cellulose and allied bodies, presumably concerned in 

 the formation of the bacterial cell membrane. The demonstration of 

 these substances has been successful only in isolated cases and has not 

 found universal confirmation. 



Glycogen-like substances have been demonstrated, according to 

 A. Fischer, 1 in B. subtilis and B. coli. These bacteria stained a reddish 

 brown color when stained with iodin, and after treatment with weak 

 acids were shown to contain dextrose. 



The bacterial ash, remaining after removal of other substances, con- 

 gists largely of phosphates and chlorides of potassium, sodium, cal- 

 cium, and magnesium. 



Osmotic Properties of the Bacterial Cell. Like all other animal and 

 vegetable cells, the bacterial cell forms in itself a small osmotic unit 

 which reacts delicately to differences of pressure existing between its 

 own protoplasm and the surrounding medium. The perfect and normal 

 morphology of a microorganism, therefore, can exist only when the 

 osmotic pressure within the protoplasm of the cell is isotonic or equal 

 to that of its own environment. The changes produced in the morpho- 

 logical relations of a cell when transferred from one environment into 

 another of varying osmotic pressure, depend intimately upon the 

 " permeability " of the cell membrane for different substances. When 

 such a membrane is permeable for water and not for substances in solu- 

 tion, it is technically spoken of as " semi-permeable." Now, as a matter- 

 of fact, the bacterial cell membrane is easily permeable for water, but 

 its permeability differs greatly in various species of bacteria for other 

 substances. Thus, for instance, the cholera vibrio shows great perme- 

 ability for common salt and B. fluorescens liquefaciens shows a lower 

 permeability for potassium nitrate than do many other bacteria. 2 



When a microorganism is suddenly removed from an environment 

 of low osmotic pressure into one showing a high pressure, say, from a 

 dilute to a concentrated solution of NaCl, an abstraction of water from 

 the cell occurs, with a consequent shrinkage of the protoplasm away 

 from the cell membrane. This process is spoken of as "plasmolysis." 

 Cell death does not usually occur with plasmolysis, but by slow diffusion 

 of the salt itself into the protoplasm, the equilibrium may eventually 

 be restored and the normal morphology of the cell resumed. In all cases 



1 A. Fischer, " Vorlesungen tiber die Bakt.," Jena, 1903. 



2 Gottschlich, in Fliigge, " Mikroorganismen," i, p. 91. 



