EFFECTS OF REORGANIZATION 339 



ence in intensity between parent and offspring becomes more pro- 

 nounced. The young ex-con jugant returns to the full capacity 

 of the species while the parent protoplasm shows the vitality 

 characteristic of its age. The difference between them is now 

 beyond the range of fluctuating variations or of experimental error 

 and furnishes unmistakable evidence of rejuvenescence. Series 7, 

 11, 24, 27, 28, 29, 30, 31, 36, 57, and 63, which exceed their parents 

 in rate of division by from 8 to 10 divisions per ten days, illustrate 

 this point, and reference to column 6 shows that these series came 

 from parents well along in age. With extremely old parents finally 

 the difference in intensity between parents and offspring reaches its 

 maximum and if parents have less than 35 divisions subsequent to 

 their age at the time of conjugation (column 7), the offspring have 

 an intensity of from 11 to 16 divisions per ten days more than the 

 parent protoplasm (Series 8, 15, 39, 63). 



3. Relative Vitality of Different Series and Effect of Parents' Age 

 on Vitality of Offspring.— Do ex-conjugants from old parents have 

 as much vitality as do ex-conjugants from young parents? That is, 

 is the organization of offspring affected by the depleted vitality 

 of the parent? Except in extreme cases these questions cannot 

 be answered by comparison of the intensities of vitality of the two 

 series. For example a series living two hundred days and dividing 

 300 times would have an average intensity of vitality indicated 

 by 15 divisions in ten days; another series living only fifty days 

 and dividing only 75 times likewise has an intensity of 15 divisions 

 per ten days. It would be far from exact to say that the two series 

 have the same vitality; here the time factor or endurance is not 

 taken into account. Hence to compare vitalities of two different 

 series both intensity and endurance must be represented. The 

 method adopted (Calkins, 1920) rests on the principle of reference 

 to a common, ideal life cycle represented by a numerical constant. 

 The number of generations by division and the days of life of a 

 series have a definite relation expressed by a percentage of such 

 an ideal constant. Such percentages indicate the relative vitality 

 of the different series and are listed in column 2 of the table. 



With these percentages expressing relative vitality it is possible 

 to compare different series in respect to the effect of age of parents 

 on the vitality of offspring. There is unmistakable evidence con- 

 tained in the table that offspring from old parents in the great 

 majority of cases have a much lower relative vitality than do the 

 parental series, or series from young parents. This is best illustrated 

 by instances where two or more offspring series are taken off at 

 different periods in the life history of the same parent. Such a 

 sequence is illustrated by Series 2,3,6 and 8, all of which came from 

 Series 1, and with a difference of 28.7 per cent in relative vitality 

 between the first (Series 2) and the last (Series 8) offspring. Another 



