ENDOMIXIS IN PARAMAECIUM AURELIA 37 



2) Is endomixis an evidence of depression or a means of 

 rejuvenescence? 



1. Can endomixis be experimentally induced? In order to 

 gain further evidence on this point I have performed a series of 

 experiments using the daily isolation method of culture, and em- 

 ploying cells of the same ancestry, on the one hand for the ex- 

 periment, and on the other for the control. 



Popoff's work tends to show that various end products of 

 metabolism, such as C0 2 , NH 3 and even CO(NH 2 ) 2 may induce 

 multinuclearity. Woodruff ('11) has shown that excreta of 

 Paramaecium are depressing agents, lowering the division rate, 

 and Woodruff and Erdmann (I.e., p. 485) have briefly stated that 

 staleness of culture medium hastened the onset of endomixis in 

 P. aurelia. In order to ascertain whether such depressing agents, 

 namely excreta, serve to induce multinuclearity or at any rate to 

 increase the frequency of its occurrence, I have carried several 

 lines of Paramaecium in culture fluid containing large amounts of 

 excreta for several weeks, and then have changed the culture to 

 fresh medium in which excreta were present in small quantities. 

 I have further carried sister lines in parallel cultures, one of 

 which contained more, and the other less excreta. The amounts 

 of excreta employed varied in the different experiments, but in no 

 case have I attempted to measure the exact amount used. In 

 some experiments I have merely left the animal on the same 

 slide, removing as much as possible of the old, and adding fresh 

 culture daily, and occasionally transferring it to a fresh slide, 

 when the old one became too foul with Bacteria. In another I 

 have used an old culture in which Paramaecia and other Infusoria 

 and Bacteria had lived for many months and from which they 

 had finally almost or entirely disappeared. The fresh culture 

 medium employed except as otherwise noted was a 0.025 per 

 cent beef extract solution in ordinary distilled water. 



It is true that the excreta employed in these experiments 

 were not derived from Paramaecium alone. Bacterial products 

 were present in all, and excreta of several other species of Infu- 

 soria in some of the experiments. The point is immaterial, 

 however, as what I have endeavored to determine is whether 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 24, NO. 1 



