586 Lorande Loss Woodruff. 



mann ('76), that in infusorian cultures after a number of genera- 

 tions the organisms are reduced in size and show other signs of 

 degeneration, were evidence in favor of Dujardin's theory. 

 As is well known, however, Weismann ('84) greatly elaborated 

 the theory of the potential immortality of unicellular organisms, 

 maintaining, on a priori grounds, that the Protozoa, like the 

 germ-cells of higher forms, are not subject to natural death. 

 Maupas ('88; '89) in his classic researches on the life-history of 

 Infusoria brought forward data which weighed heavily against 

 Weismann's hypothesis. In his long-continued cultures he found 

 marked evidence of "senile degeneration" and he confirmed the 

 general conclusion of earlier workers as to the cyclical character 

 of the life-history of certain species. More recently still Joukow- 

 sky ('98) and Simpson ('01) have investigated the life-histories 

 of various forms, and Calkins ('02, i, 2, 3; '04, i) in a series of 

 papers on Paramoecium has submitted strong evidence that this 

 species passes through more or less regular periods of vigor and 

 weakness, the periods of weakness invariably ending in the death 

 of the culture unless the organisms are "stimulated" by conjuga- 

 tion or by changed environment. This work, besides throwing 

 light on the role of conjugation in the life-cycle, gave the first 

 experimental proof that various stimuli will "rejuvenate" the 

 lagging functions of exhausted protoplasm and incite the Para- 

 mcecia to further periods of reproductive activity. 



In the light of the previous investigations on the physiology of 

 Infusoria, the following questions seem to be of sufficient impor- 

 tance to warrant still more extensive experimental work on dif- 

 ferent forms, in order to place the problems involved on a broader 

 foundation: 



1. Does the life-history of Infusoria, in general, run in cycles.^ 



2. If so, will changes in the environment bring about renewed 

 activity during depression-periods.^ 



3. Will conjugation effect "rejuvenation".^ 



4. What are the physiological and morphological changes, 

 if any, characteristic of declining vitality.^ 



5. What effect has initial and daily application of various 

 stimuli on the division-rate, /. e., on the metabolic activity of 

 protoplasm 1 



6. Is the division-rate affected by light? 



The present investigation is an attempt to answer these ques- 



