CLASSIFICATION OF THE BACTERIA 19 



are used also as generic names. When used in a simple 

 descriptive sense they are not capitalized. When used as 

 the names of genera they are capitalized and are generally 

 written in italics. 



Structure of the Bacterial Cell and Its Appendages. 

 The bacterial cell is a comparatively simple structure. It 

 possesses a definite cell wall. This may be surrounded by 

 various layers of gelatinous material or by membranes, 

 termed capsules or sheaths. It contains the protoplasm or 

 living cell material and various other cell inclusions, and 

 it may be motile by means of flagella. 



The Cell Wall. Each bacterial cell is surrounded by a 

 relatively firm membrane or cell wall. Its composition ap- 

 parently is not uniform among all bacteria. In a few cases 

 the cell wall will give the microchemical reaction charac- 



FIG. 4. CAPSULES OF VARIOUS BACTERIA. 1. Capsulated diplcrccfccus. 

 2. Capsulated streptococcus. 3. Capsulated bacilli. 3a, Bacilli 

 with asymmetric capsules. 



teristic of cellulose, indicating a close relationship in com- 

 position to the cell walls of higher plants. Most bacteria 

 are supposed to have cell walls which are somewhat chiti- 

 nous, that is, they are nitrogenous in nature. Chitin is 

 closely related to the carbohydrates. When hydrolyzed it 

 breaks down into glucosamine and acetic acid. The cell wall 

 generally is thin and layers cannot be differentiated. 



Cell Capsules and Sheaths. Some species of bacteria 

 secrete large amounts of gelatinous material about the cell. 

 In some cases this dissolves relatively rapidly in the medium 

 in which the organism is growing, sometimes making it 



