REJUVENESCENCE 71 



unicellular animals, and kept the descendants isolated, in order to 

 prevent fertilization, through3i6, 319, etc., generations of simple 

 division. Toward the end of the time the cells became reduced 

 in size and abnormal in structure through loss of cilia and other 

 organs, and all finally died under conditions similar to senile 

 degeneration in higher animals. Many other types of Infusoria, 

 also, have been watched through many hundreds of generations 

 by different observers, but the physiological activities in every 

 such experiment save one, weakened, and sooner or later, 

 abnormal or deformed specimens brought the race to an end. 

 The one apparent exception is the case of Paramecium aurelia 

 which Woodruff has carried on for many years (over 6000 

 generations) without conjugations. At regular intervals, 

 however, the race of Paramecium under observation showed a 

 reduced vitality as measured by the division rate, and it was 

 found that, during these periods of depression, the macronu- 

 cleus breaks up into fragments, and the micronuclei divide. 

 New macronuclei develop from some of the products of division 

 of the micronuclei, functional micronuclei from others, while 

 some degenerate. The fragments of the old macronucleus 

 and the degenerating micronuclei are absorbed in the cytoplasm, 

 and this addition of relatively large quantities of nucleo-proteins 

 makes a decided change in the chemical organization of the en- 

 tire protoplasm. As a result of this process of nuclear and cyto- 

 plasmic reorganization which Woodruff calls endomixis, all of 

 the vital activities are accelerated so that the organisms grow 

 and divide at a more rapid r,ate than during the process of 

 endomixis or just prior to it. This high vitality then gradu- 

 ally decreases until the next period of depression when the 

 process of endomixis is repeated. 



In essence, therefore, it appears that the unicellular organisms 

 agree with the multicellular in possessing physiological powers 

 which gradually wear out. To be sure, the single cells of the 

 majority of generations do not die. They cease to live as the 

 same cells, but the protoplasm continues to live in the daughter 

 cells arising from divisions ; but the same is true of any individ- 

 ual cell of a metazoon, since the adult organism is formed by 



