PERIODIC REORGANIZATION IN PARAMAECIUM 427 



qua non for the life of the Infusoria seemed to be placed upon a 

 firm empirical basis. 



A series of careful investigations by R. Hertwig ('00-04) and 

 Calkins ('02-'04) confirmed Maupas' general conclusion that In- 

 fusoria after a more or less definite number of divisions degen- 

 erate and finally die if conjugation is prevented. Further, the 

 latter author found that artificial stimuli of different kinds may 

 be substituted with success for conjugation since by the oppor- 

 tune use of artificial stimulation he was able to prolong the life 

 of one culture of Paramaeeium caudatum to the 742d gener- 

 ation. This significant discovery that the death of infusorian cul- 

 tures, bred on a more or less constant medium of hay infusion, 

 may be temporarily deferred by artificial means was corroborated 

 by Woodruff ('05). 



Enriques ('03) studied the same general problem and reached 

 the conclusion that the degeneration and death observed by 

 Calkins and others was due to the presence of bacterial poisons 

 in view of the fact that he succeeded in breeding Glaucoma 

 scintillans for 683 generations without signs of degeneration 

 when this factor was eliminated. Although Enriques' interpre- 

 tation of the cause of degeneration in Calkins' cultures is open 

 to question, the significant fact remains that he kept his ani- 

 mals nearly twice as long as did Maupas or Calkins without 

 conjugation or artificial stimulation, thus suggesting that degen- 

 eration is not inevitable, and that if suitable conditions are 

 supplied reproduction by division can proceed indefinitely 



The problem was attacked from another point of view by 

 Woodruff (1907 to date) who investigated the possibihty that 

 the degeneration observed in the previous investigations was 

 induced by too great uniformity in the conditions of culture, 

 or by the culture medium being deficient in something essential 

 for the continued well-being of the organisms. A race of Para- 

 maeeium aurelia (I) was isolated and bred on infusions of various 

 materials found in the natural environment of the animal, while 

 a sub-culture was subjected to the relatively constant hay in- 

 fusion culture conditions employed by Calkins ('04). The result 

 was that the cells bred in the constant hay infusion medium died 



