RELATIONS OF THE COCCACE^ 39 



Chapter VI. We still feel that the combination of chain 

 formation, with the production of large zooglea masses, 

 the growth under saprophytic conditions, and active fer- 

 mentative powers, constitutes a well-marked natural group. 



The genera Planococcus and Planosarcina, founded 

 upon the single characteristic of the possession of flagella, 

 seem on the other harid of somewhat doubtful value. 

 The slow revolution and steady translation observed 

 by Ali-Cohen and Migula as associated with flagella, is 

 certainly a phenomenon distinct from the irregular vibra- 

 tory and rotary movements noted by other observers. 

 True motility appears in a few, and only in a few, cocci; 

 but the resemblance between motile and non-motile forms 

 is so close in all other characters that this property 

 scarcely seems of generic importance. 



These considerations led us at first to recognize five 

 genera among the Coccaceae: Diplococcus, Streptococcus, 

 Micrococcus, Sarcina, and Ascococcus; and these genera 

 appeared to be arranged in a natural serial order. 

 Diplococcus is strictly parasitic and commonly produces 

 only aggregates of two cells. Streptococcus, also nor- 

 mally parasitic, thrives better, tho still not luxuri- 

 antly, on artificial media, and its typical growth form 

 is a chain. Both these genera form acid in sugar media. 

 Micrococcus includes both pathogenic and non-patho- 

 genic forms, but all grow abundantly on gelatin and agar, 

 in rather large, irregular cell aggregates, while some 

 produce acid, and some, alkali, in milk. Sarcina shows 



