18 ESSENTIALS OF BACTERIOLOGY. 



De Bary's System. De Bary divides bacteria into two groups, 

 those arising from or giving rise to endospores and those devel- 

 oped from arthrospores. This division has a more scientific 

 value than the first. 



FIG. 1. 



Micrococcus. Spirillum. Bacillus. 



Structure. Bacteria are cells ; they appear as round or cylin- 

 drical of an average diameter or transverse section of 0.001 mm. 

 (=1 micromillimeter), written 1 p.. The cell, as other plant- 

 cells, is composed of a membranous cell-wall and cell-contents ; 

 "cell-nuclei" have not yet been observed, but the latest re- 

 searches point to their presence. 



Cell- Wall. The cell-wall is composed of plant cellulose, which 

 can be demonstrated in some cases by the tests for cellulose. 

 The membrane is firm and can be brought plainly into view by 

 the action of iodine upon the cell-contents which contracts them. 



Cell-Contents. The contents of the cell consist mainly of 

 protoplasm, usually homogeneous, but in some varieties, finely 

 granular, or holding pigment, chlorophyll, granulose, and sul- 

 phur in its structure. 



It is composed chiefly of mycoprotdn. 



Gelatinous Membrane. The outer layer of the cell-membrane 

 can absorb water and become gelatinoid, forming either a little 

 envelope or capsule around the bacterium or preventing the 

 separation of the newly-branched germs, forming chains and 

 bunches, as strepto- and staphylo-cocci. Long filaments are also 

 formed. 



Zooglcea. When this gelatinous membrane is very thick, irre- 

 gular masses of bacteria will be formed, the whole growth being 

 in one jelly-like lump. This is termed a zoogloea (w, animal, 

 $, glue). 



Locomotion. Many bacteria possess the faculty of self-move- 



