PERIODIC REORGANIZATION OF P. CAIDATUM ()1 



animals ai'e placed in tiny tulies of culture nKnliuni, instead of 

 on slides, so that the volume of culture medium is somewhat 

 greater, but not large enough to render it impossible to control 

 them daily and so detect conjugation if it occurs, then the ani- 

 mals apparently can live indefinitely. This i-esult is, in general, 

 in accord with the earlier observations of Woodruff ('lie, p. 64) 

 though at that time he used somewhat larger volumes of medium 

 to save the Paramaecium caudatum and so was not able to 

 positively prove that conjugation did not occur. 



It has seemed best to consider this point in justification of 

 our resorting to material from tiny tube cultures for certain 

 stages of the reorganization process. But we would emphasize 

 that many of the stages of this process in Paramaecium caudatum, 

 as all of the stages of the process in Paramaecium aurelia, have 

 been secured from daily isolated pedigreed animals so that it 

 is absolutely positive that the phenomenon under discussion 

 occurs in caudatum as in aurelia at clearly defined periods. To 

 repeat — we have shown, by the isolation slide method, the physio- 

 logical characteristics of the reorganization process in the re- 

 current rhythms of the division rate, and the accompanying 

 cytological changes of this process to the climax at the low points 

 of the rhythms. The completion of the process in isolated slide 

 animals is evident from the completion of the rhythms in many 

 cases. But owing to the longer rhythmic periods in Paramaecium 

 caudatum as compared with Paramaecium aurelia, and owing 

 to the lesser viability of the former species and the smaller 

 number of generations over which its reorganization process 

 extends, we did not secure all of the later cytological changes 

 from isolated slide animals but resorted to carefully controlled 

 'tube' animals as already described. AVe will grant that the 

 original discovery of the reorganization process in Paramaecium 

 caudatum would have been more difficult than it was in Para- 

 maecium aurelia because of the longer rhythmic period in the 

 former species and its less marked viability under the arti- 

 ficial slide pedigreed method during the crucial stages of the 

 phenomenon. 



