PERIODIC REORGANIZATION IN PARAMAECIUM 477 



perature will change the division rate. Indeed it may be said 

 that the rate of reproduction is a function of the environment 

 of the cell — ^except as the rhythms interfere — and consequently 

 the fluctuations which appear in the graph of the division rate 

 of a culture are not, ipso facto, true rhythms, i.e., due to "inherent 

 rhythmical changes in the phenomena of the cell'' (Woodruff and 

 Baitsell 'lib, p. 357). 



The present cytological study demonstrates the nature ol the 

 inherent changes in the cell which have their obvious physio- 

 logical expression in the rhythms of the rate of reproduction. 



The relations of the process to these fluctuations can be most 

 readily appreciated by a consideration of graphs of the rate of 

 divisions of Lines VI and III of Sub-culture IE, which was sub- 

 jected to the constant culture medium of beef extract and to 

 practically constant temperature conditions (about 26°C.) with- 

 in the optimum zone for this race. 



The five-day period was adopted in the presentation of our 

 results because this was the method of constructing the graph 

 emphasized in the original study of rhythms in this culture. 

 It is realized, of course, that a five-day period is largely an 

 arbitrary one and that the ideal graph would present the momen- 

 tary changes in the metabolism of the cell. Data for such a 

 curve being absolutely impossible to secure, it might seem at 

 first glance that the daily record of division would approach 

 most nearly to this ideal condition. As a matter of fact, the 

 twenty-four-hour period is as arbitrary as the five-day period 

 when it is considered that this is a long period when compared 

 with the metabolic changes in the cell and that the daily record, 

 made at approximately 11 a.m., would merely give the divisions 

 actually completed during the previous twenty-four hours. For 

 example, let us assume that, at the time of isolation, two animals 

 are present, representing one division during the previous twenty- 

 four hours. The record for that day is one division. One ani- 

 mal is then isolated and it divides within an hour and each of the 

 resulting cells again divide twice before the next isolation. The 

 record for this second day is three divisions, thus the record for 

 the two days shows a different division rate for each day, i.e., 



