PHYSIOLOGICAL VARIATIONS IN PARAMECIUM 507 



believe this to be the sole reason for the longevity of Woodruff's 

 cultures. In the first place, Woodruff's are the first observations 

 that have been made on isolated Paramecium aurelia and its 

 life history is unknown. In the second place, the food of his 

 race has probably remained the same despite the varied medium. 

 Not only are the infusions open to the air of the laboratory but 

 with each transference the new medium is seeded with bacteria 

 from the old. His long continued culture, therefore has been 

 subject to the same chance of bacterial poisoning that Calkins' 

 cultures were, but his race is still flourishing and the explanation 

 must lie in the makeup of the organisms themselves rather than 

 in the method employed. This conclusion is reached by Wood- 

 ruff ('09, p. 03) who believed there are "strong and weak strains 

 among infusoria" and it is strengthened by his later experiences 

 ('11) with Paramecium aurelia which he maintained for several 

 months without apparent loss of vitality on a constant medium 

 of beef extract. Woodruff is confident that his race will live in- 

 definitely: "I believe this culture shows clearly that Paramecium 

 aurelia when subjected to suitable culture conditions, has the 

 power of unlimited reproduction by division without conjugation 

 or artificial stimulation" (Woodruff, '11 p. 266), and again ('11, 

 p. 141) "The conclusion seems justified that this culture of Para- 

 mecium (aurelia) can, in all probability, be continued indefinitely 

 on this 'constant' medium (beef extract)." We do not share his 

 optimism, however, and can only say that while his results are 

 remarkable, his race is not yet dead. Is there any clue to the par- 

 ticular makeup of this race of Paramecium aurelia? 



B. Are all Paramecia potential germ cells? 



Woodruff ('09) states that he may have been fortunate in ob- 

 taining a particularly strong race in his long culture. "I would 

 not suggest that the protoplasm of every wild Paramecium has 

 the potential to attain over twelve hundred generations or more." 

 (p. 303). This statement appears to strike the right pitch in the 

 disharmony of results achieved in these various observations on 

 the life history of the Infusoria. Differences in individuals se- 



