32 WiNSLOW : A statistical criterion for bacteria 



The result of this condition of affairs is that systematic bacteri- 

 ology has almost fallen into desuetude. After a brave beginning 

 In the way of describing bacterial species the conviction gradu- 

 ally gained ground that of the making of species there is no end. 

 Aside from the forms which are recognized by their association 

 with well-defined diseases, there are hardly a score of bacteria 

 that can be distinguished with any certainty among the hun- 

 dreds which have been already described. Time and industry 

 alone would be needed to produce as many thousands as there are 

 now hundreds of paper species; but the condition of affairs would 

 only be still more hopeless. 



Refuge from the multitude of varieties has been sought, on the 

 one hand, by ignoring all minor differences and massing the bac- 

 teria into a few main groups ; and, on the other hand, by a frankly 

 arbitrary schematic arrangement of cultures according to their 

 pi us-or- minus reaction in a few standard media, decimal numbers 

 being used for the description of each combination of possible re- 

 actions. Neither of these expedients is very satisfactory. The 



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ical importance. The second method, while convenient for the 

 cataloguing of descriptions, only obscures the natural phylogenetic 

 relationships of bacterial types. Organic individuals have not been 

 created in symmetrical groups, differing in the presence or absence 

 of character A, each group including two sub-groups, respectively 

 possessing and lacking character\6. They have been developed 

 along irregular and complex lines, and are now related in family 

 groupings of infinitely various kinds and degrees. 



There is one method, and apparently only one, which promises 

 to answer the puzzling question of bacterial relationships. This 

 is the statistical method. If attention be given, not to the indi- 

 vidual, but to the group, and if certain characters are quantita- 

 tively measured in a considerable series of cultures and statistically 

 analyzed, order begins to emerge from chaos. Almost every de- 

 gree of acidity or gelatin liquefaction may be found in some indi- 

 viduals ; but the greatest number of strains group themselves 

 about well-defined centers. The curve of frequency plotted for 

 any character shows certain modes which are the types about 

 which the bacteria as a group are varying. Furthermore, if sev- 



