EFFECTS OF REORGANIZATION 335 



taneonsly and under identical conditions in isolation cultures. 

 If such conjugations occur early in the life history of the parent 

 series both parent and offspring run simultaneously for some months; 

 if late in the life history of the parent the offspring series outlives 

 the parent, in some cases for many months. An arbitrary test 

 of the difference in vitality of parent and offspring is furnished by 

 a comparison of the division-rate of the ex-conjugant for its first 

 sixty days of life with the division-rate of the parent during the 

 same calendar sixty days. The difference between the two rates 

 indicates the difference in intensity of vitality between parent and 

 offspring. In the accompanying synoptic table data are listed for 

 all series from 1 to 120, including series number, relative vitality 

 (column 2), number of generations attained (column 3), number of 

 division days (column 4), parent series (column 5), age of parent 

 series at time of conjugation (column 6); number of divisions of 

 parent subsequent to conjugation (column 7); intensity of vitality 

 of parent and offspring and differences between these intensities 

 (columns 8, 9 and 10). The division-rates represent the numbers of 

 divisions which any individual of a series would undergo in ten days. 



The last column of the table on pages 336, 337 and 338 gives an 

 emphatic affirmative to the question: Does conjugation effect a 

 renewal of vitality? 



2. Intensity of Vitality and Extent of Renewal. — An important 

 matter which is usually overlooked in experiments of this nature 

 is the intensity of vitality of the parent protoplasm at the time of 

 offspring-forming conjugations. The metabolic activity, growth 

 and reproduction, of an organism are not unlimited, each species 

 having its limit of vitality. As more water cannot be forced into a 

 jug that is already filled, so it is impossible, under constant tempera- 

 ture conditions, to increase vitality in protoplasm that is already 

 functioning to its full capacity. In Uroleptus, however, conjugations 

 do not occur when the protoplasm is at its maximum of vitality 

 and the difference in intensity of vitality between parent and 

 offspring depends upon the age of the former at the time of con- 

 jugation. With offspring from young parents the parental vitality 

 is relatively high and the difference in intensity for the first sixty 

 days of life of the offspring between parent and offspring is fre- 

 quently so small as to fall within the limits of fluctuating variations 

 or of experimental error. This was the case for example in Series 

 2, 4, 64, 71, 78, 79, 85, 96, 97, 102, 104, and 111 where the difference 

 in intensity is less than two divisions in ten days. Reference to col- 

 umn 6 of the table shows that all of these series came from young 

 parents. Such slight differences afford little positive evidence of 

 rejuvenescence and failure to take into account the age of parents 

 explains a number of discordant results in the literature of this 

 subject. With advancing age of the parent protoplasm the differ- 



