1915] Lorande Loss Woodruff 373 



was inherent, indicated that it is the composition of the medium, 

 rather than the changes in the medium, which is conducive to the 

 unhmited development of this race without the necessity of conju- 

 gation or artificial Stimulation, 



From a study of various species of hypotrichous infusoria, as 

 well as the main culture of ParamcEcium aurelia, it was found that 

 minor periodic rises and falls of the division-rate occur, from which 

 recovery is autonomous. These fluctuations were termed * rhythms ' 

 and contrasted with the so-called cycle, which comprises a varying 

 number of rhythms and, according to Maupas and Calkins, ends in 

 the death of the race, if conjugation or artificial Stimulation is not 

 resorted to. 



The problem of rhythms was then studied intensively.^ It was 

 found that the subjection of the culture to the most constant en- 

 vironmental conditions failed to eliminate the rhythms and thus to 

 resolve the graph of the multiplication rate into an approximately 

 straight line; but, instead, the rhythms appeared slightly more pro- 

 nounced. It was also found, from a study of the temperature co- 

 efficient^ of the rate of reproduction of the culture, that this is influ- 

 enced by temperature at a velocity similar to that for a chemical 

 reaction, except when the rhythms interfere. Thus, it is apparent 

 that there are inherent rhythmical changes in the phenomena of the 

 cell which produce slight fluctuations in the division-rate. 



The results, then, from the study of this pedigreed race of 

 Paramcociwn aurelia led us to conclude that this organism, when 

 subjected to suitable culture conditions, has the power of unlimited 

 reproduction by division without conjugation or artificial Stimula- 

 tion; the only necessary Variation in the rate of reproduction being 

 the normal minor periodic rise and fall of the division-rate, due to 

 some unknown factor in cell phenomena, from which recovery is 

 autonomous (rhythm). 



Calkins,^ however, did not share this optimism and sought the 

 explanation, of the diametrically opposite results derived from his 

 and from our cultures of Param<^cium, in variations in the tendency 



2 Woodruff and Baitsell: Journ. of Exp. Zool., 1911, 



3 Woodruff and Baitsell: Am. Journ. Physiology, 191 1. 

 * Calkins: Journ, of Exp. Zool., 1914. 



