222 GEORGE ALFRED BAITSELL 



time (November 20, 1913), a period of more than twenty-two 

 months, under these same conditions. 



The method of carrying a test tube culture has already been 

 described above (see Culture Obtt, p. 217) and this same method 

 has been used in this case, except that the medium used has been 

 hay infusion instead of the beef medium. 



At any time during the period that the culture has been under 

 observation it has been possible to secure almost any number of 

 animals simply by inoculating a suitable medium with a few of 

 them from the regular test tube culture. Great numbers of the 

 animals obtained in this way have been used in class work, for 

 the study of both living and prepared material, during the course 

 of the experiments, and no abnormal specimens have ever been 

 found. In order to test the division rate of the animals from 

 this culture after they had been subjected to the culture condi- 

 tions described above for ahnost twenty months, a daily isola- 

 tion culture on the hay infusion medium was started on July 

 8, 1913, and continued for a period of 35 days. In starting it, 

 one individual was taken from this test tube culture and placed 

 on a depression slide. During the night this individual divided 

 twice, forming four animals, and these were isolated and placed 

 on depression slides to start the four lines of the daily isolation 

 culture. During the 35 days that this culture was under obser- 

 vation, the animals maintained a division rate of almost exactly 

 2.5 divisions per day. It is evident from this experiment that 

 the animals of this culture are capable of maintaining as high a 

 division rate now as when the culture was first started. 



The animals of this test tube culture have given at all times 

 during the more than 22 months that they have been under 

 observation every evidence of being in an environment which is 

 entirely suitable for them and it is believed that these animals 

 can be bred indefinitely under these conditions without conjugation 

 or artificial stimulation of any kind. 



To summarize briefly the culture work with this race of Pleuro- 

 tricha lanceolata: Two daily isolation cultures and one mass cul- 

 ture in test tubes were carried, namely: Culture Ph, a daily iso- 

 lation culture which attained 656 generations in a period of 259 



