GENERIC CHARACTERS IN THE COCCACEAE 153 



is necessary to eliminate properites which are due mainly to the char- 

 acter of the medium and the conditions of incubation. As we shall 

 show later, those minute differences in the appearance of colonies on 

 gelatin which form the basis for a large number of German descrip- 

 tions, fall mainly under this head. Secondly, many characters, while 

 really belonging to the organism itself at a given moment, are so 

 easily modified by cultivation under other conditions as to be prac- 

 tically worthless in systematic work. Among the cocci, pathogenicity 

 is a property of this sort. In the third place, it is evidently unfair 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 which the cells readily sepa- 

 rate exhibit a more diffuse turbidity. Plate cultures add little more 

 information than may be obtained by a careful scrutiny of stabs and 

 streaks; and the growth on potato and blood serum in many groups 

 of bacteria, and particularly among the cocci, are only valuable as 

 measures of that extremely fugitive quality, the general vigor of the 

 culture. 



The considerations which have influenced us in the selection 

 of characters for study among the Coccaceae may be conveniently 

 arranged in the order, and under the headings, of the Report of the 

 Committee on Standard Methods of Water Analysis to the Labora- 

 tory Section of the American Public Health Association (1905). 

 3. MORPHOLOGICAL CHARACTERS. 



Form. The form of the individual cell furnishes no help in the 

 classification of the Coccaceae, since under favorable conditions 

 all appear as regular spheres. Irregular oval forms occur at times, 

 particularly in cultures freshly isolated from the throat or alimentary 

 tract, but the form usually becomes normal after cultivation. 



Manner of grouping. The grouping of the cell elements offers 

 a character of considerable importance among these bacteria. While 

 the cocci do not exhibit an entirely unchanging form of grouping, 

 the individuals do show a distinct tendency to occur in one of four 

 forms either in pairs, chains, masses, or packets. 



