12 



THE AMERICAN NATURALIST [Yol.LVI 



produced in some frequency by an agency which takes 

 the matter at once out of the field with which I am dealing 

 —by the recombinations occurring at conjugation, at bi- 

 parental reproduction. Our monstrous stock may have 

 come from such an individual, included by accident in the 

 experiment. Our spirit-stirring results faded into noth- 

 ingness—a type of what has so often happened in promis- 

 ing work in the inheritance of environmental effects, of 

 what will probably often happen again. 



Other workers have been more successful. In 'the bac- 

 teria, if we can accept the accounts given by many investi- 

 gators, and well summarized, for example, in Adami's 

 "Medical Contributions to the Theory of Evolution," 

 environmental conditions frequently alter, in an adaptive 

 way, the persisting characteristics of the stocks, differen- 

 tiating a single race into several. The difficulties of cer- 

 tainly working with unmixed strains is very great in these 

 minute creatures, a fact which leads many students of 

 experimental evolution to reject generalizations based on 

 these organisms. Further, the extraordinary work of 

 Lohnis (1921), recently published by the National 

 Academy, tends, if substantiated, to so completely upset 

 all supposed knowledge of life history in the bacteria that 

 it will be best to omit these from consideration until the 

 air is cleared. For similar reasons, and from considera- 

 tions of space, I will not speak of the work on pathogenic 

 Protozoa. 



Turning then to those larger organisms that are iso- 

 lated with as much ease as are guinea pigs, Middleton has 

 found that differences of vigor and of rate of reproduction 

 are produced by subjection of infusoria for long periods 

 to diverse temperatures, and are perpetuated, after 

 equalizing the temperatures, from generation to genera- 

 tion for long periods, and through the process of conju- 

 gation. At this meeting he has reported similar results 

 piodiUMd hy subjection to diverse chemicals. How far 

 thi> i> cHiiipai'.iblc to change of other characteristics than 

 reproductive vigor we do not know. 



