1 6 Society for Experimental Biology and Medicine. 



ing by simple division, offer the same protoplasm for study gen- 

 eration after generation, and with each division the daughter 

 organisms, by reason of the functions of regulation and regenera- 

 tion, perfect themselves in the race-type, while digestion, assimila- 

 tion, waste, repair and growth are handed down unchanged from 

 cell to cell. The problem is to ascertain whether these various 

 functions will continue their activities indefinitely or whether proto- 

 plasmic old age will supervene to put an end to the race. In 

 nature such an end is prevented by sexual union, whereby the 

 conjugating organisms are rejuvenated. 



In the experiments by the author this function was prevented 

 by isolation. The general metabolic functions wore out four con- 

 secutive times at intervals of six months, and each time, except 

 the last, the race was saved only by a change in diet or by chem- 

 ical stimuli. The phenomena were analogous to those in the 

 artificial fertilization experiments of Loeb and others, with this 

 difference, that if comparable with artificial parthenogenesis, the 

 process was repeated with the same protoplasm three consecutive 

 times. In the fourth period of degeneration the stimuli previously 

 tried were no longer effective and the race died out, seven hundred 

 and forty-two generations old. Structural changes were different 

 in the different periods of depression. The degenerate animals, 

 in the periods which were successfully overcome, had curiously 

 altered nuclei and endoplasm. In the last period of depression 

 which was not overcome, the nucleus and endoplasm were normal, 

 while abnormal parts were found in the micronucleus and the cor- 

 tical plasm. 



The conclusions which this part of the work seems to justify 

 are : 



1. That " old age," so-called, of the cell may be due either 

 to the wearing out of functions, or to the degeneration of structural 

 parts. The former is capable of artificial rejuvenescence, the latter 

 apparently not. 



2. The ordinary functions of metabolism, such as digestion, 

 assimilation, excretion, growth, etc., are dependent upon certain 

 definite portions of the cell (macronucleus and endoplasm), while 

 the dividing energy is a function of the micronucleus and of the 

 cortical plasm. 



