BACTERIAL CLASSIFICATION 7 



the type seems in stable equilibrium. In other groups 

 racial variations are almost infinite in number. Gotsch- 

 lich (1903) holds that this latter condition is charac- 

 teristic of organisms in the presence of a new environ- 

 ment; and Andre wes and Horder (1906) point out 

 that the genera in which varieties are most numerous 

 are the dominant genera, the groups which are at the 

 moment succeeding in the struggle for existence. Kruse 

 (1896) emphasizes the fact that variations are most 

 marked under unfavorable conditions and particularly 

 under conditions which permit of slow multiplication. 

 Plating out old cultures, for example, shows numerous 

 variations. On the other hand rapid transfers in a 

 single medium tend to eliminate aberrant forms and 

 to produce a homogeneous race, adapted to the par- 

 ticular medium in question. Thus our ordinary culture 

 methods tend to eliminate variations which would 

 naturally occur and produce an artificial uniformity and 

 constancy. 



Among the higher animals and plants racial variations 

 appear to be of two general types, continuous or fluctuat- 

 ing variations, and discontinuous sports or mutations. 

 It is probable that variations of both kinds occur among 

 the bacteria, altho careful study of heredity among 

 these organisms is wofully deficient. Dyar (1895) long 

 ago made a beginning in this direction; but only a 

 beginning. He believed that he had observed both 

 "slight, continuous variations" and "sports or discon- 



