474 BIOLOGY OF THE PROTOZOA 



cultures with this organism obtaining a vitaHty curve similar to 

 that found liy Woodruff (see, however, below). Oxytricha fallax 

 has been similarly studied by Enriques (1905), by Woodruff' (1906) 

 and by Baitsell (1914). The first gives no detailed account of his 

 cultures but makes the general statement that this and other 

 organisms cultivated by him are capable of multiplying asexually 

 ad infinitum. Woodruff, however, finds a definite curve of vitality 

 similar to that of Pkurotricha with a waning vitality and ultimate 

 death after 860 generations by division, and Baitsell followed the 

 history of three cultures all showing the typical life history, one 

 dying out in the 131st generation, a second in the 159th, a third 

 in the 150th, while a fourth culture in test tubes lived for a longer 

 period but it also finally died, none of these cultures approaching 

 the long history of Woodruff^'s strain. Styloriychia jmstulata also 

 has been cultivated by Enriques (1905) and by Baitsell (1912), 

 the former giving no statistical data but maintaining that division 

 can go on indefinitely without degeneration or conjugation if the 

 conditions are right. The latter follows out the history in isolation 

 cultures and finds a typical curve of vitality (Fig. 198) with waning 

 vitality ending in death, in the longest line after 572 generations. 

 In other organisms Woodruff' (1905) found waning vitality and 

 death in Gastrostyla steinii after 288 generations, and Gregory 

 (1909) a similar result with Tillina magna after 548 generations and 

 Calkins (1912) a similar result with Blepharisma undulans after 

 224 generations. 



In all of the cases cited above the organisms under investigation 

 are bacteria feeders, and despite the daily change of medium and 

 care in maintaining the isolation cultures the old criticism of bac- 

 terial poisoning or deleterious eff'ects of the medium has been 

 repeatedly advanced. Woodruff', however, has kept Paramecium 

 aurelia continuously living for seventeen years on the same bac- 

 teria diet, "endomixis" occurring at stated intervals and the same 

 observer using the same methods has followed other organisms 

 through periods of waning vitality and death. Metalnikov (1919) 

 similarly has continuously cultivated Paramecium caiidatum without 

 conjugation. It seems highly probable, therefore, that the preven- 

 tion of death has little to do with the environment in these experi- 

 ments but lies in the organisms themselves— with Paramecium in 

 the phenomenon of "endomixis." 



More direct evidence that bacteria contamination is not respon- 

 sible for the ultimate death in isolation cultures is afforded by 

 similar experiments with carnivorous ciliates. With these it is 

 possible to use bacteria-free culture media in which the food organ- 

 isms are introduced with the experimental individual. Again in 

 the majority of cases the ultimate result has been the same as with 

 bacteria eaters. Thus Actinobolus radians was followed through 



