EFFECTS OF REORGANIZATION 333 



in ex-conjugant and parental cultures it is evident that conjugation 

 directly induces not only an immediate acceleration of reproduction 

 but also an acceleration which persists at least as long as the life 

 of the parental cultures. These results are in opposition to all 

 results which indicate that conjugation is devoid of a profound 

 physiological stimulation of the metabolic activities of the cell 

 expressed in reproduction" {Joe. tit, p. 189). Thus in Spathidium 

 spathula not only are the division-rates of ex-conjugants higher 

 than those of the parental strains but the ex-conjugants actually 

 outlive the parent protoplasm, hence the authors further conclude: 

 ''Conjugation typically has a high survival value in the life of the 

 organism" (p. 196). 



It is significant that Woodruff and Spencer studiously avoid use 

 of the term "rejuvenescence" in their work. They speak of an 

 increased division-rate of ex-conjugants and of the "survival value" 

 of conjugation but not of renewal of vitality. As these are the two 

 essential factors which characterize the phenomena of rejuvenes- 

 cence we are justified in including Woodruff among the proponents 

 of rejuvenescence. The two factors were discussed in an earlier 

 analysis of rejuvenescence (Calkins, 1920) in which it was pointed 

 out that the division-rate expresses the "intensity" of vitality and 

 the length of life in division days the "endurance;" the latter is 

 evidently the same as Woodruff and Spencer's "survival value." 



The experimental work on Spathidium spathula was a confirma- 

 tion of the work on Uroleptus mobilis which was begun in 1917. 

 A single ex-conjugant was the progenitor of all the material that 

 has formed the subject of the investigation. The method employed 

 throughout was the usual isolation culture method (see p. 248). 

 In the following account of the experiments the term "series" 

 always means an ex-conjugant with the progeny formed from it 

 by division; the progeny being represented by five pure lines which 

 are continued by isolation cultures until vitality is exhausted and 

 death ensues. Conjugation tests at regular intervals provide 

 material for filial series. Up to January 1, 1925, 125 different 

 series had been studied; 116 of them had followed the usual history 

 and had died out and 9 series were under culture. The last of 

 these 9 series represents the F 29 generation of successive conjuga- 

 tions since the original ex-conjugant was isolated. Abundant statis- 

 tical data were accumulated during these seven years and these 

 furnish valuable evidence in favor of the theory of rejuvenescence. 



The analysis of this evidence has been the subject of many 

 papers by numerous writers (Calkins, Woodruff, Jennings, Robert- 

 son, et al.) from which the general conclusions may be drawn that 

 renewal of vitality follows conjugation, and that the extent of 

 renewed vitality as well as the continued vitality depend upon the 

 age of the parental protoplasm at the time of conjugation. The 



