122 GAEY N. CALKINS 



of the life history of parental series and at different stages of 

 vitality, so that I have abundant data for the study of com- 

 parative vitality of parent and offspring. It is with pleasure, 

 based upon admiration for the genius of that gifted pioneer in 

 this field of research, Edouard Maupas, that I can say these data 

 convincingly prove the truth of his conclusions that conjugation 

 in ciliates restores vitality and prevents the phenomena accom- 

 panying 'old age' which we include under the terms senescence 

 and natural death, 



METHODS AND RECORDS 



On October 3, 1917, a rich culture in an old hay infusion was 

 found to contain a large number of individuals of Uroleptus 

 mobilis. The normal structure of this rare cihate is described 

 and its systematic position given in my earlier paper. It is 

 illustrated again in figure 1 of the present paper. Attempts were 

 immediately made to cultivate the organism on the usual hay- 

 infusion culture medium. A better medium was obtained by 

 mixing boiled flour water, hay infusion, and spring water, and 

 this was used until the middle of January, 1918. It was in this 

 medium that the first pairs of conjugating individuals were 

 found and isolated, giving the ex-conjugant destined to form the 

 first, or A series. A still better medium was substituted on Jan- 

 uary 18th. This was obtained by boiling 100 mg. of chopped 

 hay with 130 mg. of flour in 100 cc. of spring water, and diluting 

 this, when twenty-four hours old, with an equal part of fresh 

 spring water. This standardized medium, made fresh each day, 

 has been used exclusively throughout the experiments. 



Series and lines 



As used here, the term 'series' is applied to an aggregate of 

 individuals, all derived from a single individual and representing 

 its protoplasm. An ideal way to study vitality of such proto- 

 plasm at difi"erent age periods would be to follow all of the progeny 

 throughout the life cycle. As this is obviously impossible, I 

 follow as many individual representatives of that protoplasm as 

 time and space will permit. My practice is as follows: When 



