1912] Lorande Loss Woodruff 397 



when this animal had produced four individuals, each of these was 

 isolated on a separate slide to form the four lines of the culture, 

 Paramcocium aurelia I. The culture has been maintained by the 

 isolation of a specimen from each of these lines practically every 

 day up to the present time, thus precluding the possibility of con- 

 jugation taking place between sister cells. The number of divisions 

 of each line has been recorded at the time of isolation and the 

 average rate of these four lines has been again averaged for vary- 

 ing numbers of days as the exigencies of the different experiments 

 demanded. Permanent preparations have been preserved from time 

 to time for the study of the cytological changes during the life 

 history.^ During the first eight months the culture medium con- 

 sisted of infusions of hay and fresh grass, but from February, 

 1908, to the present time a more varied medium has been used. It 

 was found that this race of Paramcocium would live in nearly any 

 Infusion of materials collected in swamps and ponds, and therefore, 

 in an endeavor to supply as far as possible all the Clements which 

 may be encountered in the usual abode of the organism, materials 

 were collected practically at random from ponds, hay infusions, 

 laboratory aquaria, etc. The infusions were thoroughly boiled to 

 prevent the contamination of the pure lines of the culture by foreign 

 strains. This culture of Paramcscium has afforded an unfailing 

 supply of free living cells for the experiments to be described. It 

 is obvious that all the observations were made on the "same 

 protoplasm." 



Among the fundamental problems whose Solution has been 

 sought by numerous investigators of the Protozoa is that of proto- 

 plasmic old age, and the possible relation of conjugation to proto- 

 plasmic * rejuvenation.' More than thirty-five years ago Bütschli 

 and Engelmann observed that in infusoriancultures, after a number 

 of generations, the organisms are reduced in size and show other 

 signs of degeneration, and this afforded the first important experi- 

 mental data which were advanced against the prevailing opinion 

 that the Protozoa, because of their comparatively simple structure 



* Woodruff : ParamcEcium aurelia and Paramcecium caudatum. Journ. 

 Morphology, vol. 22, no. 2, 191 1. 



