CHAPTER II. 



Morphology' of the bacteria — Grouping — Mode of multiplication 

 — Spore-formation — Motility. 



In form the bacteria are unicellular, and are seen to 

 exist as spherical, rod- or spindle-shaped bodies. They 

 always develop from preexisting cells of the same char- 

 acter and never appear spontaneously. 



The classifications of the older authors were upon 

 purely morphological peculiarities, and in consequence, 

 were more or less complicated. The present tendency 

 is to simplify this morphological classification, and to 

 bring the bacteria into three great groups, with their 

 subdivisions ; each group comprising those members 

 whose individual outline is that either of a sphere, a 

 rod, or a spiral. 



To these three grand divisions are given the names 

 cocci or micrococci, bacilli, and spirilli. 



In the group miorococd belong all spherical forms, 

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

 are of equal diameter in all directions. 



The bacilli comprise all oval or rod-formed bacteria. 



To the spirilli belong all organisms which are twisted 

 in the form of a corkscrew. 



The micrococci are subdivided according to their 

 grouping, as seen in growing cultures : into staphylo- 

 cocci — those growing in masses like fish-roe or clusters 

 of grapes ; streptococci — those growing in chains con- 



' Morphology, pertaining to shape ; outline. 



