VITALITY 



473 



ued study of the life history of Paramecium aurcUa which he began 

 ill 1907, and which had been generally hailed as giA'ing positive proof 

 of the correctness of Weismann's point of view. Parthenogenesis, 

 however, has the same effect upon organization and upon vitality 

 that conjugation has, and as Woodruff and Erdmann showed that 

 "endomixis" occurs approximately once in thirty da^>s in Para- 

 mecium aiireJia and about once in sixty days in Paramecium can- 

 datum, any experiments and observations on vitality are valuable 

 only as they lie within these limits of time. For this reason many 

 of the conclusions of Hertwig (1889), of Joukowsky (1898), of 

 Calkins (1903, 1904, 1913) and of Jennings (1909, 1913) drawn from 

 observations on Paramecium are of questionable value, and should 

 be used cautiously in connection with the present problem. In 

 other forms however, analogous reorganization processes occur 



4.0 

 3.5 

 3.0 

 2.5 

 2.0 

 1.5 

 1.0 

 .5 

 .0 



Fig. 200. — Vitality graph of Spathidium spathiila. (After Woodruff.) 



during encystment and are thus advertized in cultures whereas 

 Paramecium does not encyst at all but continues under conditions 

 of low vitality to live and move during such periods of depression 

 when "endomixis" is taking place. 



While the list of recent experimenters with the Infusoria is rather 

 a long one the actual number of different organisms studied is 

 comparatively small, but different experimenters working with the 

 same species obtained strikingly similar results. Thus Pleurotricha 

 lanceolata has been studied by Joukowsky (1898) and by Woodruff 

 (190G), the former following out four series, three of which died out 

 after approximately 220, 250 and 442 generations without conjuga- 

 tion while a fourth was abandoned after 458 generations. Woodruff, 

 using the daily isolation method, found a gradually waning vitality 

 with ultimate death. Baitsell (1914) also carried out isolation 



