592 Lorande Loss Woodruff. 



During period five there was a marked rise for no apparent 

 cause to over two and one-eighth divisions, and then a fall to 

 about seven-eighths of a division per day in the seventh period, 

 which was below the lowest rate so far attained by the culture. 

 The next fall, however, was still lower, when seven-tenths of a 

 division per day was recorded. After this there was another 

 rising period extending over about a month and attaining a 

 maximum rate of nearly two divisions. From here there was a 

 gradual decline for four periods when a minimum of six-tenths of a 

 bipartition per day was averaged — the lowest point so far attained. 

 Again a slight rise for twenty days, and then a fall at the twenty- 

 first period (210 days since the culture was started) to one- 

 quarter of a division per day, the lowest point reached in the 

 division-rate, which had been gradually diminishing since the 

 beginning. 



It was apparent that unless something was done to stay this 

 decline or "rejuvenate" the culture at this point that it would 

 soon die out. Calkins had succeeded in reviving Paramoecium 

 cultures with an extract of beef, and acting on this clue all four 

 lines were transferred to weak beef-extract^ for five days and then 

 changed back to the regular hay-infusion diet. As the beef- 

 extract showed no immediate results, flour and water was tried 

 again, apparently to no purpose. I now returned to beef-extract, 

 this time making it stronger and varying the strength from day 

 to day, and this treatment was continued up to June i. This 

 time a very slight rise in the division-rate for the period occurred 

 [cf. Diagram I, period 22) and during the following ten days it 

 increased to almost one division per day. Then it fell again for 

 two periods, but the slowest rate here attained was considerably 

 faster than the previous low mark of period 21. In period 26 the 

 diagram shows a considerable rise which was brought about by a 

 sudden springing into activity of one line (A-i) of the culture. 

 Instead of dividing at the rate of about once in two days, it started 

 off on July 7 at the rate of three times per day. When I first noted 

 this sudden change I thought that possibly in some way, in spite of 

 all precautions, an adventitious specimen, perhaps as a cyst, had 



'The beef-extract was made by boiling for a few minutes a piece of lean beef about the size of a silver 

 half-dollar in 200 cc. of tap-water. This was allowed to settle for a number of hours and then the clear 

 extract was used. 



