230 GEORGE ALFRED BAITSELL 



from unsuitable culture conditions but since none of the media 

 supplied happened to be entirely suited to the needs of the 

 organism, death invariably resulted after a time. 



From the results of these experimental studies mentioned above 

 it is believed that only one conclusion can be drawn and that is 

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

 soria, as in Paramaecium, is not a question of senescence or, in 

 other words, a tendency of the protoplasm to grow old, but it is 

 dependent upon whether or not the organisms are supplied with an 

 environment which is adapted to their particular requirements. 

 Given a species which is adapted to the culture conditions in 

 which it is bred there is reason for believing that it can be bred 

 indefinitely without the necessity of conjugation or of artificial 

 stimulation. If the culture conditions supplied are unfavorable 

 to the organism, marked nuclear and cytoplasmic degenerative 

 changes occur and the death of the culture inevitably results, 

 sooner or later, depending upon the degree to which the condi- 

 tions are unfavorable, the natural resistance of the species, and 

 its ability to adapt itself to the new conditions. 



VI. GENERAL SUMMARY 



1. The object of these experiments was (1) to determine if 

 culture conditions could be supplied to the hypotrichous Infu- 

 soria which would eliminate the so-called life cycle in these forms, 

 and (2) to observe the effect, upon the life history of the organ- 

 isms studied, of the various culture conditions supplied. 



2. Three media were used in these experiments, namely, a 

 'constant' medium consisting of a 0.025 per cent solution of 

 Liebig's extract of meat, a hay infusion medium, and a Varied 

 environment' medium. Both daily isolation cultures and mass 

 cultures kept in test tubes were employed in this work. 



3. Four cultures of Oxytricha fallax have been under obser- 

 vation, all of which were started from descendants of an original 

 individual isolated from a laboratory hay infusion, October 19, 

 1911. Culture Ob was started October 19, 1911, and was carried 

 until February 10, 1912, on a beef extract medium, when it died 



