150 C.-E. A. WINSLOW AND ANNE F. ROGERS 



variations which rightly deserve generic and specific names, although 

 records of the characters of individual races by the decimal system 

 are of the greatest value in mapping out intermediate regions. Only 

 the statistical study of numerous individuals by comparable quan- 

 titative methods can reveal the general laws of natural classification 

 among the bacteria; and this study must be made in each group 

 with an open mind free from arbitrary predispositions. 



We desire in advance to deprecate a comparison between the 

 present work and the numerous detailed and exact biometrical stud- 

 ies which have appeared in other fields. In bacteriology our methods 

 of measurement are crude and tedious, and the general knowledge 

 requisite for the selection of a homogeneous mass of material is lack- 

 ing. We should know the outlines of the general groups of the 

 cocci, for example, before we can properly select material to study 

 variation in any one of them. 



II. METHODS OF THE INVESTIGATION, 

 i. ISOLATION OF CULTURES. 



With regard to the larger groups of the Coccaceae we have else- 

 where shown (Winslow and Rogers, 1905) that the family could 

 be divided into two subfamilies and five genera, defined as follows: 



Subfamily i, Paracoccaceae (Winslow and Rogers): Parasites 

 (thriving only, or best, on, or in, the animal body). Thrive well 

 under anaerobic conditions. Many forms fail to grow on artifi- 

 cial media; none produce abundant surface growths. Planes of 

 fission generally parallel, producing pairs, or short or long chains. 



Genus i, Diplococcus (Weichselbaum) : Strict parasites. Not 

 growing, or growing very poorly, on artificial media. Cells normally 

 in pairs surrounded by a capsule. 



Genus 2," Streptococcus (Billroth): Parasites (see above). Cells 

 normally in short or long chains (under unfavorable cultural con- 

 ditions, sometimes in pairs and small groups, never in large groups 

 or packets). On agar streak effused, translucent growth, often 

 with isolated colonies. In stab culture little surface growth. Sugars 

 fermented with formation of acid. 



Subfamily 2, Metacoccaceae (Winslow and Rogers): Facultative 

 parasites or saprophytes. Thrive best under aerobic conditions. 



