WiNSLOW: A STATISTICAL CRITERION FOR BACTERIA 39 



bacteria, according to the lines followed in recent evolution. The 

 classificatory value of a particular character must be determined 

 for each group by a preliminary survey of its relationships. 



3» The most satisfactory method of studying the systematic 

 relations of these simple and variable forms is by obtaining quanti- 

 tative measurements of a number of characteristic properties in a 

 large series of individuals and by statistical analysis of the results. 



4. Generic names may conveniently be given to the larger 

 groups of organisms having several apparently independent prop- 

 erties in common, as indicated by correlation between different 

 measurements. Generally these groups will be found associated 

 with certain definite habitats. 



5. Specific names may be reserved for the smaller groups, 

 characterized by variations in single uncorrelated properties* 

 Each strongly marked mode on the curve of frequency, marking 

 a type center about which variations are occurring, may be taken 

 as a species. 



6. Genera and species defined in this manner by frequency of 

 occurrence are not invalidated by the variability of the organisms 

 belonging to them. Stable or unstable, they are definite realities, 

 and their recognition makes it possible to arrange the bacteria in 

 convenient natural groups which approximate their true phylo- 

 genetic relationships. 



Biological Laboratories, 



Massachusetts Institute of Technology, 



Boston, Massachusetts. 



