BACTERIAL CLASSIFICATION 3 



number of species among the pneumococci and the 

 streptococci. 



Under a given set of conditions many characters of 

 many bacteria exhibit extraordinary constancy. From 

 a broad viewpoint the fixity of type among these simple 

 organisms is as remarkable as the deviations from it. 

 Even such minute differences as are implied in the spe- 

 cific resistance of certain strains to unfavorable environ- 

 mental conditions are transmitted unchanged for many 

 generations. Yet the effect of previous variation is 

 clearly seen when a number of different strains are com- 

 pared. Such an examination discloses, not a few well- 

 marked species, but an indefinite series of intergrading 

 varieties. 



For these reasons the science of systematic bacteri- 

 ology has remained in a notably undeveloped state. A 

 score of large groups of bacteria have been more or less 

 satisfactorily recognized (Fliigge, 1896). Certain of 

 these groups, like those of the aerobic spore-formers, the 

 colon bacilli, and the diphtheria bacilli, doubtless repre- 

 sent true natural families or genera. In one such group, 

 that of the aerobic spore-formers, where appreciable 

 morphological differences exist, the species and varieties 

 have been carefully worked out by Chester (1904). 

 For the most part, however, specific names among 

 the bacteria mean less than nothing. The incomplete 

 description of a vast number of identical or minutely 

 differing forms has led to a confusion auite bewildering 



