COMPARATIVE STUDY OF THE COCCI 45 



which the cells readily separate 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 growths on potato and blood serum in 

 many groups of bacteria, and particularly among the 

 cocci, are only valuable as measures of that extremely 

 variable 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 Laboratory Section 

 of the American Public Health Association (1905). 



Morphological Characters. 



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 

 cells 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. Individual cultures exhibit a 

 distinct tendency to occur in one of four forms — either 

 in pairs, chains, masses, or packets. The grouping is 

 somewhat influenced by the age of the culture, and by 

 the kind of medium on which it is grown; and even the 



