44 RELATIONSHIPS OF THE COCCACE^ 



solid media and are most active at a temperature of 37 

 degrees. This fact must be taken into account in inter- 

 preting our results. For Micrococcus and Sarcina, how- 

 ever, the series should be fairly representative. 



The characters ordinarily used in descriptive bacteri- 

 ology are few enough, particularly in a group of such 

 simple morphology and limited biochemical powers as 

 the Coccaceae. This number must be still further 

 reduced, however, when we come to inquire which of 

 them really indicate constant and independent varia- 

 tions. In the first place, it is necessary to eliminate 

 properties which are due mainly to the character of 

 the medium and the conditions of incubation. Minute 

 differences in the appearance of colonies on gelatin, 

 which form the basis for a large number of German 

 descriptions, fall mainly under this head. Secondly, 

 many characters, while really belonging to the organism 

 itself at a given moment, are so easily modified by culti- 

 vation under other conditions as to be of minor value 

 in systematic work. Among the cocci, pathogenicity is 

 a property of this sort. In the third place, it is obviously 

 unnecessary to give independent weight to characters 

 which are simply the indirect result of other properties 

 already recorded. Thus among the cocci differences in 

 broth cultures are closely connected with the size of the 

 cell aggregates. Organisms growing in large groups, like 

 most of the sarcinae, produce heavy sediment and often 

 colony-like groups on the walls of the tube, while those in 



