ZOOLOGY: C. ZELENY 
487 
THE EFFECT OF SUCCESSIVE REMOVAL UPON THE RATE 
OF REGENERATION 
By Charles Zeleny 
ZOOLOGICAL LABORATORY. UNIVERSITY OF ILLINOIS 
Received by the Academy. July 15. 1916 
One of the most interesting facts in connection with regeneration 
is the ability to replace a part after repeated removal. Former studies 
by the writer show that as a rule the rate of regeneration following a 
removal is no greater than that following second and later removals if 
the effect of age is eliminated. Where a difference exists it is in favor 
of the later regeneration. 
The matter is of very great interest in connection with general prob- 
lems of development and particularly in connection with the question 
as to the existence or non-existence of a necessary limit to the amount 
of living substance that a single individual may produce during its 
life cycle. Does the production of a group of tissues use up a part 
of a certain store of developmental energy possessed by the individual 
or is this store inexhaustible or perchance even increased by exercise 
of the function? These questions warrant more extended study espe- 
cially in view of the additional analysis that has been made of other factors 
controlling the rate of regeneration. The new data support the con- 
clusion previously reached and make possible a further analysis of the 
character of the difference between successive regenerations. 
In making a comparison of successive regenerations a method must 
be devised for eliminating the effect of age. If the rate of a second 
regeneration is compared with that of a first regeneration in the same 
individual any difference that is made out may be due not to the pure 
effect of successive injury but to the effect of difference in age. 
The method pursued in the present experiments consists in the initial 
removal of a portion of the tail in one-half of a set of Amphibian larvae 
of equal age. When regeneration has proceeded for several days there 
is a second removal of the part accompanied by a first removal in the 
half of the set that had not previously been operated upon. The sec- 
ond regeneration that ensues in one-half of the set may be compared 
directly with the first regeneration in the other half. There is no 
difference in age. 
In experiment I approximately one-half of the tail was removed in 
tadpoles of the green frog, Rana clamitans. At six days the average 
first regeneration length is 2.01 mm. and the average second regenera- 
tion length 2.18 mm. The first exceeds the second in five sets and the 
