148 GARY N. CALKINS 



period of the filial series than during the first sixty days. Indeed 

 the discrepancy between parent and offspring in successive sixty- 

 day periods increases in geometrical proportion. Thus the dif- 

 ferences between the A and C series for the first, second, and third 

 sixty-day periods are indicated by 1.53, 2.63, and 4.10 divisions 

 in ten days. The differences in the A-D series are 3.03, 5.77, and 

 7.09. In the C-F series, the differences for four successive 

 sixty-day periods are 1.0, 2.23, 4.63, and 7.26, which is a geomet- 

 rical increase of the disparity in division energy of parent and 

 offspring protoplasm. 



When we consider that we are dealing here with one protoplasm 

 derived from the protoplasm of the single individual ex-con jugant 

 that was isolated on November 16, 1917, these results offer con- 

 clusive evidence that conjugation rejuvenates or restores vi- 

 tality to an optimum when that vitality is reduced through 

 continued metabolic activity. Many series have died, but I 

 have under cultivation to-day protoplasm of the L, N, P, 0, and 

 R series which is directly descended from the original ex-con jugant 

 A and which is living with the same metabolic vigor as that shown 

 by the A series during its most vigorous period. Yet there has 

 been no change in the standardized culture medium with which 

 this protoplasm has been fed, and no variation in the daily 

 treatment. The continued vitality is due solely to the successive 

 conjugations which have taken place between representative bits 

 of this protoplasm. 



Since one condition, viz., starvation, is found in the conju- 

 gation tests and not in the isolation cultures, the objection might 

 be raised that changes may be set up in the protoplasm due to 

 such starvation or to some other condition of the conjugation 

 tests which would result in a restoration of vitality, thus making 

 conjugation an accessory phenomenon without effect on rejuve- 

 nescence. To test this point twenty individuals which had 

 reached this starvation point as shown by reduced size, and all 

 taken from a conjugation test, but without having conjugated, 

 were isolated and carried on in isolation cultures as though they 

 were ex-conjugants. An ex-con jugant from the same test, and 

 obtained from a pair that were isolated while conjugating, was 

 likewise carried on at the same time in five lines as series U. 



