EEJUVENESCENCE IN UROLEPTUS MOBILIS 123 



an initial individual divides, each of the two cells is isolated as 

 the beginning of a 'line;' when these divide, two more lines are 

 started, and one more is added at the next division. Each day 

 a record is made of the number of divisions during the twenty- 

 four hours in each line, and a single individual is isolated with a 

 capillary pipette from each line and transferred to fresh culture 

 medium. The vitality is measured by the division rate, the 

 average number of divisions per day in all five lines for a given 

 period representing the vitality of the series for that period. I 

 have daily records, extending from November 16, 1917, to date, 

 of sixteen series and eighty lines of Uroleptus. 



Conjugation tests 



In every line of a series at the time of the daily isolation there 

 are two or more individuals in the culture dish according to the 

 number of divisions that have occurred. After one is transferred 

 the unused individuals are either thrown away or placed in a 

 similar culture dish containing about 1 cc. of the fresh culture 

 medium. Representatives of all five lines of a series are collected 

 in this way and stored in a moist chamber as 'stock.' Here 

 they accumulate by division until a large number are present. 

 Once a week this stock is washed into a Syracuse dish contain- 

 ing several cubic centimeters of fresh culture medium and set 

 aside as a conjugation test. The number of individuals increases 

 rapidly until, in three or four days, there are many hundreds or 

 even thousands of organisms. These Syracuse dishes are ex- 

 amined carefully every other day for a period of two weeks and 

 without any fresh medium being added. During these two weeks 

 the limited food is gradually exhausted, and by the end of the 

 period conjugation would have occurred if the internal condi- 

 tions of the organisms were suitable for it. The date of the 

 appearance of conjugations is recorded and the extent of conju- 

 gations, up to epidemic frequency. At the end of the period 

 the individuals are small, inactive, and starved, and, other tests 

 being under way, they are discarded. 



