14 RELATIONSHIPS OF THE COCCACE^E 



classificatory significance in one place may be almost 

 valueless in another." In studying any one group it 

 is therefore necessary to examine afresh each of the 

 various characters used for the identification of bacteria 

 in general, to determine its local value and significance. 

 After this has been done the selected characters should 

 be studied by exact and definite methods in a consider- 

 able series of cultures. Finally, the results may be 

 analyzed with two ends in view. First, each center of 

 numerical frequency, marking a group of organisms vary- 

 ing about a distinct type in regard to a single definite 

 property, may be recognized as a species. Second, those 

 species which are bound together by the possession of a 

 number of similar properties may be constituted as genera, 

 and larger groups of genera, still characterized by some 

 characters in common, may receive the rank of families or 

 subfamilies. 



It cannot of course be expected that the correlation 

 of characters in bacteria shall be absolute. It is not 

 absolute in any group. For example, among verte- 

 brates, the correlation of a hairy coating with the bring- 

 ing forth of living young is one of the characteristic 

 marks of the Mammalia. Yet the Echidna and the 

 Ornithorhynchus are classed as mammals tho they lay 

 eggs. So, among the bacteria, correlations vary in 

 different individuals, those properties generally corre- 

 lated appearing in certain organisms in exceptional 

 combinations. If, however, we consider, not the single 



