THE STRUCTURE OF BACTERIA. 3 



In the simplest and smallest of living things, 

 visible only with the aid of the microscope, the 

 entire body consists of a single cell. The 

 bodies of all the larger and higher forms of 

 life are built up out of structural units similar 

 to these independent cell-organisms. All cells 

 are essentially minute masses of a substance 

 called protoplasm, a semi-solid, gelatinous sub- 

 stance which, viewed with the ordinary micro- 

 scope, is apparently homogeneous, but which, 

 according to Altmann, consists of small 

 granules of an albuminous nature, embedded 

 in a similar, structureless albuminous matrix. 

 These elementary granules or granula, are 

 often arranged in threads, sometimes in such 

 a way as to form a sponge-like network or 

 reticulum ; Butschli, however, regards proto- 

 plasm as essentially a liquid, possessed of a 

 foam-like or " honeycomb " structure. On Alt- 

 mann's view, the " granule " is the vital unit,, 

 and a cell in its simplest form is to be regarded 

 as a colony of such " elementary granules " 

 rather than as a true physiological and mor- 

 phological unit. But, as a matter of fact, the 

 cell is the simplest and lowest form of living 

 thing now known, a true " elementary organ- 

 ism " (Briicke) or " seat of life " (Virchow). 

 Growth and reproduction, which we recognize 

 as conspicuous phenomena of life, are always 



