228 GEORGE ALFRED BAITSELL 



termed 'typical life cycle' curves. Also the study of the pre- 

 pared material, from the cultures of both species which died out, 

 reveals morphological and nuclear changes which can be inter- 

 preted as being due to 'senile degeneration.' However, since, 

 as has been noted above, 'sister cells' from the test tube cultures 

 of Oxytricha fallax, preserved at the same time or even later 

 than cells in a degenerate condition taken from the daily isola- 

 tion cultures and which should, therefore show at least as great 

 a degeneration, reveal a normal nuclear and cytoplasmic condi- 

 tion and, also, because of the fact that in Pleurotricha lanceolata 

 no degenerate or abnormal individuals have ever been found in 

 the test tube culture during the entire period that it has been 

 under observation, it is evident that the atypical conditions 

 that were present in the cells of the cultures which died cannot 

 be attributed to an inherent condition of senescence. The results 

 obtained clearly indicate that the degenerative changes which 

 occurred and the subsequent dying out of the cultures resulted 

 not from a condition of 'senile degeneration' in the animals, 

 but from the fact that the culture conditions supplied in these 

 cases were not entirely suitable, and consequently, it is believed, 

 that the length of the so-called life cycle in these hypotrichous 

 infusorian forms is hot a question of an inherent ability to attain 

 only a certain number of generations, but it is dependent upon 

 the degree to which the culture conditions are favorable. If the 

 conditions supplied are entirely adapted to the needs of the organ- 

 ism, as in the test tube culture of Pleurotricha lanceolata, it seems 

 evident that there will he no so-called life cycle and the organism 

 will continue to multiply as long as these conditions are maintained. 



When the results of some of the earlier investigators which 

 support the view that the Infusoria possess a definite life cycle 

 ending at a certain number of generations are considered, it 

 appears that these results have been due to the cumulative 

 effects of culture conditions which were to some degree unsuit- 

 able to the organisms under observation and which, therefore, 

 were not adapted to their indefinite existence. 



The question of artificial stimulation as a means of prolonging 

 the so-called life cycle of various protozoan forms should also 



