CLASSIFICATION OF MICROORGANISMS 77 



tion of Migula's scheme, but with some changes which seem to 

 coordinate it better with practice. A key to the various groups 

 and genera of the bacteria as here used will first be given, fol- 

 lowed by a brief discussion of the characteristics of the more 

 important genera. All of those groups of bacteria which are 

 not of economic importance or which have no pathogenic members 

 have been eliminated. This removes some fifteen or eighteen 

 genera which have no common or economic representatives and 

 are chiefly of systematic or botanical interest. 



KEY TO THE GROUPS AND GENERA OF BACTERIA 



I. Order Eubacteria, or true bacteria. Cells free from sulphur. 

 Family I. Coccaceae. Bacterial cells globular when in a free state. 



Xon-motile. 



Cell division occurring in parallel planes resulting in the formation of 



chains Streptococcus. 



Cells dividing in two planes, forming plates of cells, or not remaining 

 united, or dividing irregularly to form irregular masses. .Micrococcus. 

 Cell division occurring in three planes, all at right angles, the cells re- 

 maining united after division and forming cubes or packets. .Sarcina. 

 Motile. 



Same as Micrococcus, but with organs of motion Planococcus. 



Same as Sarcina, but with organs of motion Planosarcina. 



Family II. Bacteriaceae. Cells cylindric in shape and not bent . . Bacillus. 



Family III. Spirillaceae. Cells in the form of corkscrews or spirals, or 



segments of a spiral. Cells fairly rigid, usually motile by means of a 



flagellum or tuft of flagella at the end Spirillum. 



Cells forming long, thin, and tenuous spirals. Flagella, if present, 

 demonstrated only with difficulty. Probably protozoa in part and 



not true bacteria Spirochceta. 



Family IV. Chlamydobacteriaceae. Cells cylindric, united in threads, 

 and surrounded by a sheath. Arthrospores sometimes present. 



Filaments show no branching Leptothrix. 



Filaments show false branching Cladothrix. 



Filaments show true branching. 



Arthrospores or conidia produced Xocardia. 



;>ores observed Actinomyccs. 



II. Order Thiobacteria. Cells containing sulphur granules. 



Filaments surrounded by a sheath Thiothrix. 



Filaments not surrounded by a sheath Beggiatoa. 



Streptococcus. The term Streptococcus is applied to any 

 spherical organism whose cells occur in chains. The method of 

 development has already been discussed. Spores are not developed. 

 In some forms the chains break up readily into pairs, to which 



