REPRODUCTION OP THE HYPOTRICHOUS INFUSORIA 229 



be mentioned. Calkins ('02), for example, has shown in his 

 work with Paramaecimn caudatum that, at times, a decided 

 change of medium may result in a 'rejuvenation' and the ani- 

 mals which before had been dividing very slowly and showing 

 other signs of degeneration, will take on a new lease of life and 

 appear normal for a time. This 'artificial rejuvenation' could 

 be accomplished a number of times but finally the organism 

 reached a stage where no 'rejuvenation' resulted from any of the 

 methods tried and the animals of the culture died out. Wood- 

 ruff ('05) also found in his work with one of his cultures of Oxy- 

 tricha fallax that these animals were 'artificially rejuvenated' 

 by the use of a beef extract medium. At about the 300th gen- 

 eration, after the culture had been under observation for about 

 ten months, the animals of the culture were dividing very slowly 

 and it seemed that they would all die, when they were 'rejuve- 

 nated' by the use of the beef extract and finally reached the 

 860th generation, almost a year later, before the culture died 

 out. At the time it was believed that the degeneration, which 

 appeared in the animals of the cultures under observation, was 

 due to an inherent condition of senescence, but it would appear, 

 from the more recent researches, that the degeneration resulted 

 from the cumulative effects of culture media or culture condi- 

 tions which were not entirely adapted to the organisms in ques- 

 tion. Woodruff in a recent paper ('13) holds this view with 

 regard to his culture of Oxytricha fallax and bases his conclusion 

 upon the results of his work with Paramaecium aurelia. To 

 quote (p. 8): 



Therefore in the light of studies during the past decade, I would 

 interpret the cycle of my Oxytricha A culture as being the result of the 

 fact that the race of Oxytricha fallax which was employed was not 

 adapted to live indefinitely 'when continuously subjected to the same 

 environment' of hay infusion ('05, p. 627). I beheve that if an entirely 

 suitable environment had been secured this culture would have given 

 evidence of unlimited power of reproduction by division without con- 

 jugation as my present P. aurelia race has done. 



In the cases of 'artificial rejuvenation,' it seems evident, then, 

 that the change of medium brought about a temporary relief 



