20 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



slimy or gelatinous in consistency. In other cases this 

 material remains attached to the cell, forming a layer of 

 greater or less thickness. This may be regarded as the 

 outer portion of a greatly swollen cell wall. Such a mass 

 is termed a capsule. This capsule is usually composed of 

 gum or gumlike material. Occasionally it is nitrogenous in 

 nature. 



A feiv filamentous or rod-shaped bacteria growing in 

 water surround themselves by a relatively firm membrane, 

 a tube in which the filaments or chain of cells lie. This tube 

 is termed a sheath. \n same species this sheath becomes 

 impregnated with iron. 



Protoplasm and Cell Inclusions. — The protoplasm or 

 living material within the bacterial cell is usually not clearly 

 differentiated as in the higher plants into nucleus and cyto- 

 plasm. Tt is probable that in most cases nuclear material, 

 that is, chromatin, is scattered more or less throughout the 

 protoplasm. Some bacteria apparently have a primitive 

 type of nucleus. 



The outermost portion of the protoplasm, that is, that 

 portion lying next to the cell wall, is differentiated as a 

 membrane termed the ectoplast. This ectoplast apparently 

 functions in determining what can enter and what can leave 

 the cell. 



Bacterial cells may contain inclusions of many kinds. 

 JMost common are granules which stain relatively deeply 

 with some of the ordinary laboratory dyes such as methylene 

 blue. Because their color reactions resemble chromatin they 

 are termed metachromatic granules. In some species of 

 bacteria vacuoles are developed. These apparently are 

 spaces in the protoplasm filled with cell sap but not with 

 living material. Each vacuole is surrounded by a mem- 

 brane of the same general type as that surrounding the 

 entire mass of protoplasm. Granules of carbohydrate are 

 observable in some bacteria. The exact composition is not 



