CHAPTER II. 



Morphology^ of bacteria— Grouping— Mode of multiplication— Spore-forma- 

 tion— Motility. 



In structure the bacteria are unicellular; they are seen 

 to occur as spherical, rod- or spiral-shaped bodies. They 

 always develop from pre-existing cells of the same char- 

 acter and never appear spontaneously. 



The classifications of the older authors and of tlie 

 botanists are usually upon purely morphological pecu- 

 liarities, and, because of slight variations that are seen 

 to occur in the size and shape of one and the same 

 species, are more or less complicated. The present 

 tendency is to simplify this morphological classification, 

 and to bring the bacteria into three great groups, witli 

 their subdivisions, the members of each group being 

 determined by their individual outline, viz., that of a 

 sphere, a rod, or a spiral. 



To these three grand divisions are given the names 

 cocci or micrococci, bacilli, and spirilla. 



In the group micrococci belong all sphericaLiorms, 

 i. e., all those forms the isolated individual members of 

 which are practically of the same diameter in all direc- 

 tions. (See Fig. 1, a, b, c, d.) 



Tlie bacilli comprise all oval or rod-formed bacteria. 

 (See Fig. 2.) 



To the spirilla belong all organisms that are curved 



1 Morphology :— pertaining to shape, outline, structure. 



