I9I2] Lorande Loss Woodruff 401 



III 



It is evident from many investigations on the life history of 

 Infusoria that these organisms in pedigree cultures exhibit minor 

 rhythmic fluctuations in the rate of reproduction. These were 

 emphasized in a study of the life history of several hypotrichous 

 Infusoria and defined as follows: "A rhythm is a minor periodic 

 rise and fall of the fission rate, due to some unknown factor in cell 

 metabolism, from which recovery is autonomous."^ 



The success with beef extract as a constant medium for Para- 

 mcscium naturally led to an intensive study of the rhythms,^ in 

 Order to determine if these can be eliminated by a still more con- 

 stant environment, i. e., whether they are due to minor variations 

 in the environment or to unknown intracellular phenomena, as 

 originally stated. 



The experiments in regard to the rhythms were begun by iso- 

 lating sub-cultures from the main sub-culture on beef extract and 

 placing the animals in a similar manner on depression slides in beef 

 extract medium. The preparations were kept in Chambers of a 

 Panum thermostat at constant temperatures within the Optimum 

 temperature zone of the organism. Every precaution was taken 

 to maintain all the conditions of the environment as constant as 

 possible.^^ 



A study of the rate of reproduction shows that the exceptionally 

 and practically constant conditions of the environment failed to 

 diminish or eliminate the rhythms — but on the contrary tended to 

 bring them out more clearly. The fact that the rhythms appear 

 more pronounced under the practically constant conditions existing 

 during these experiments than they do under ordinary laboratory 

 conditions clearly suggests that they are due to a fundamental 

 factor in cell phenomena and not to extraneous causes. For if they 

 are due to inherent intracellular conditions, one would a priori 



* Woodruff, 1905, loc. cit. 



* Woodruff and Baitsell : Rhythms in the reproductive activity of Infusoria. 

 Journ. Exper. Zoology, vol. ii, no. 4, 191 1. 



'° For details cf. Woodruff and Baitsell, loc. cit. 



