506 G. N. CALKINS AND L. H. GREGORY 



abnormal and that environmental influences bring about the 

 fatal result. Enriques, ('07) for example, kept Glaucoma scin- 

 tillans under culture for 683 generations (from Jennings '12). 

 He found that if the organisms are left in the same small culture 

 fluid for some tirne they weaken and die whereas if the medium 

 is changed every day, they continue to live and he kept different 

 organisms for long periods under these conditions without ap- 

 parent effect. He concludes, therefore, that Calkins' results with 

 Paramecium were due to the continued use of bacterial culture 

 media until the Paramecia finally succumbed to bacterial poisons, 

 but ignored the important technical point that Calkins' method 

 was the only one which he himself had found favorable for Glau- 

 coma and other ciliates, namel}^, changing the medium every day. 

 This argument is further contradicted by the results obtained 

 with other infusoria which do not live on bacteria, for example, 

 Spathidium spathula and Actinobolus radians. The former eats 

 Colpidium colpoda; the latter Halteria grandinella. In these 

 cases the organisms are kept in pure water which is changed 

 daily and a certain number of Colpidium or Halteria added to it. 

 Here no question of bacterial poisoning can enter into the prob- 

 lem, but the infusoria died nevertheless. 



Criticisms based on methods, however, were apparently sup- 

 ported by the splendid and arduous experiments of Woodruff who 

 for more than five years and a half followed the life history of 

 Paramecium aurelia through more than 3500 generations. The 

 method employed is practically the same as that used by his 

 predecessors with this difference — the infusions were made by boil- 

 ing different vegetable matters from time to time, as well as beef, 

 so. that the race of Paramecium had a variable substratum in the 

 food medium. It was argued that this change reproduced more 

 nearly the normal conditions of Paramecium than does a con- 

 stant medium of hay infusion, and that the race has continued 

 to live because of this change. 



There is reason for accepting this argument in part, for the 

 salt content of infusions from different sources undoubtedly var- 

 ies and the changes may act somewhat as did the salts and change 

 of medium in Calkins' experiments. Nevertheless, we do not 



