Microbial Structures and Staining Reactions 



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bacteria would all tend to assume a spherical shape. When it is 

 said that the wall is firm, it should also be pointed out that it is 

 somewhat elastic. Ordinary staining usually fails to distinguish 

 the wall from the rest of the cell unless the organism has been 

 grown in a concentrated solution which causes the cytoplasm to 

 shrink away from the outer wall, leaving a ghost-like shell. 



Schematic drawing of a hypothetical bacterial cell. 



Cellulose, hemicellulose, or mucin (nitrogen-containing com- 

 pounds) are the common constituents of bacterial cell walls. 



The cell wall proper is probably not as discriminatory as is the 

 underlying cell membrane, which limits the cytoplasm of the 

 organism. Because of its selectivity we refer to this membrane as 

 being semi-permeable in nature. Theories have been proposed 

 to explain this selectivity, and these explanations vary from a 

 simple mechanical sieve theory to complex physico-chemical re- 



