428 LORANDE LOSS WOODRUFF AND RH. ERDMANN 



out after a typical Calkins cycle, while those bred on the 'varied 

 environment' medium did not pass through periods of marked 

 physiological depression or show morphological changes which 

 could be interpreted as abnormal. This race is still (June, 1914) 

 in a normal condition, having attained over 4500 generations 

 without conjugation or the use of artificial stimuli. 



The success with the varied culture medium naturally led to 

 the question whether the longevity of Paramaecium on a varied 

 environment is dependent upon intrinsic stimuli from the fre- 

 quent changes of the medimn, or whether a constant medium of 

 hay infusion is unfavorable because it lacks some elements which 

 are essential for the continued existence of the organism. Ac- 

 cordingly, Woodruff and Baitsell ('11 a) bred a sub-culture of 

 this race for a period of nine months on a constant culture 

 meJium of beef extract. The continued health of the organisms 

 on this constant medium throughout the experiment, which was 

 continued sufficiently long to include a Calkins cj^cle if such was 

 inherent, indicated that it is the composition of the medium 

 rather than the changes in the medium which is conducive to 

 the unlimited development of this race without the necessity of 

 conjugation or artificial stimulation. 



From a study of various species of hypotrichous Infusoria, 

 as well as his main culture of Paramaecium aurelia. Woodruff 

 found that minor periodic rises and falls of the division rate 

 occur from which recovery is autonomous. He termed these 

 fluctuations 'rhythms' and contrasted them with the so-called 

 cycle, which comprises a varying number of rhythms and, ac- 

 cording to Maupas and Calkins, ends in the death of the race if 

 conjugation or artificial stimulation is not resorted to. The 

 problem of the rhythms was studied intensively by Woodruff 

 and Baitsell ('11 b) who showed that when Paramaecium aurelia 

 is subjected to the most constant environmental conditions it is 

 impossible to eliminate the rhythm and thus resolve the graph 

 of the multiplication rate into an approximately straight line. 

 Accordingly there are inherent rhythmical changes in the phe- 

 nomena of the cell which produce slight changes of the divison 

 rate. The same result was reached by Woodruff and Baitsell 



