PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volumes APRIL 15, 1919 Number 4 
RESTORATION OF VITALITY THROUGH CONJUGATION 
Gary N. Calkins 
Department of Zoology, Columbia University 
Communicated by Edmund B. Wilson, January 15, 1919 
The physiological effect of conjugation, or fertilization, has been interpreted, 
in the main, along two lines of theory. One of these may be indicated by 
Blitschli's term Verjiingung, and by Maupas's corresponding one rajeunisse- 
ment, terms indicating that the primary effect of conjugation is to restore 
vital activities to an optimum. The other theory, first fully elaborated by 
Weismann, assumes that the union of germ plasms (amphimixis), brought 
about by conjugation, is a source of variations. 
These theories are not reciprocally exclusive, and it is possible that both 
are correct, although neither has been conclusively established. 
Biitschli interpreted conjugation in the protozoa, as a means whereby 
waning vitality is restored to full metabolic activity. The problem thus 
suggested, involves three fundamental questions: (1) Does the protoplasm 
of a single individual protozoon and its progeny by division, undergo a pro- 
gressive waning of vital activities leading to 'old age,' degeneration, and, 
finally, to natural death? (2) Does conjugation actually restore such 
weakening protoplasm to a condition of full metabolic activity? (3) If 
conjugation accomplishes this, what is the explanation of the result? 
The first of these three questions was answered in the affirmative by the 
experiments of Maupas and of numerous subsequent investigators. The 
second has never been answered conclusively, although strong experimental 
evidence has accumulated in support of the affirmative. The third question, 
obviously, is dependent on the second and will be disregarded here. 
In the present preliminary paper, I submit the results of experiments 
made during the last year and a half, which offer a positive answer to the 
second of these three questions, affording proof that conjugation, in the cili- 
ated protozoon Uroleptus mobilis, actually restores waning vitality to full 
metabolic vigor. These results are based on the records of the progeny of a 
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