39^ Pedigrccd Race of Paramccciiim [Mar. 



and method of reproduction, are not subject to natural death. 

 Bütschli made the pregnant Suggestion that conjugation in the 

 Protozoa is essentially a process of Verjüngung, or restoration of 

 the general vitality, whereby the organisms are endowed with the 

 Potential for a new period of reproductive activity, and by analogy 

 this conception has been applied to the phenomenon of fertilization 

 in higher forms. 



A host of important studies have been made by various investi- 

 gators to test the power of the Protozoa to reproduce indefinitely 

 without conjugation, and the results secured for the most part sub- 

 stantiated the conclusion that only a comparatively limited number 

 of generations may be attained by the Infusoria without conjuga- 

 tion or artificial Stimulation.^ The first point then, toward which 

 the studies on the culture under consideration were directed, was 

 the longevity of Paramacium without conjugation or artificial 

 Stimulation. 



The results of the early experiments with this culture showed 

 that the animals could not be bred for many generations in a con- 

 stant culture medium of hay Infusion^ and consequently a varied 

 culture medium was used thereafter which comprised infusions of 

 material collected and made up as already described. In culture 

 media of this character the organisms have flourished for over four 

 and one half years and have attained, up to the present time, 2,720 

 generations without conjugation or artificial Stimulation. The ani- 

 mals are to-day in as normal morphological and physiological con- 

 dition as at the start, and the rate of reproduction, which is un- 

 doubtedly the best criterion of vitality, during the past month was 

 far above the average rate for the culture. The potential inherent, 

 so to speak, in the original cell of this pedigreed race will be ap- 

 preciated when it is recalled that theoretically the number of cells 

 produced by this organism may be represented by 2 raised to the 

 2,720th power. This result, then, establishes beyond doubt the 

 fundamental biological fact that the protoplasm of a single animal 



*Cf. Calkins: Archiv für Entwick-Mechan., 1902. 



^Woodruff: The life cycle of Paramcecium when subjected to a varied 

 environment. Amer. Naturalist, vol. 42, no. 500, 1908. Further studies on the 

 life cycle of Paramcrcium. Bio!. Bulletin, vol. 17, no. 4, 1909, p. 294. Two 

 thousand generations of Paramcecium. Archiv für Protistenkunde, Bd. 21, 

 1911. 



