144 



Scientific Proceedings (39). 



9i (50i) 



On the power of reproduction without conjugation in 

 Paramecium. 



By LORANDE LOSS WOODRUFF. 



[From the Sheffield Biological Laboratory of Yale University.] 



I have presented to this society the results obtained to May, 

 1909, on the life cycle of Paramecium when subjected to a varied 

 environment. This communication brings the results up to date 

 (May 18, 1910). 



A culture of Paramecium aurelia was started May 1, 1907, by 

 the isolation of a "wild" individual from a laboratory aquarium, 

 and it has been under daily observation during the thirty-six and 

 a half months which have elapsed since that time. Infusions of 

 hay and grass, together with any material that may be found in 

 the usual habitat of Paramecium, have been employed as a culture 

 medium. The possibility of infecting the culture with "wild" 

 strains has been avoided by boiling the infusion. Daily isola- 

 tion of an individual from each of the lines of the culture has 

 prevented the possibility of conjugation taking place, and has 

 enabled me to obtain an accurate record of the division rate. 



So far the culture has attained the 1,795th generation. The 

 average rate of division for the thirty-six and a half months has 

 been more than one and a half divisions per day. The average 

 rate for any ten-day period has not fallen as low as one division 

 in two days, while it has been for several ten-day periods more 

 than two and a half divisions per day. Therefore, since marked 

 physiological depression has not been indicated by the division 

 rate, special stimuli have not been resorted to at any time to 

 "rejuvenate" the culture. 



The results derived up to the present time from the study of 

 this culture show that under the conditions of a suitable, varied 

 environment Paramecium aurelia does not necessarily undergo 

 "cyclical" changes in general vitality, and give strong reasons for 

 believing that the life history of this organism may be of unlimited 

 duration without conjugation or artificial stimulation. 



