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ZOOLOGY: C ZELENY 
from an injured surface is not retarded by simultaneous regeneration in 
other parts of the body. Where a difference exists between the rates 
with and without additional injury there is usually an advantage in 
favor of the part with additional injury. The differences are however 
slight and in some cases come within the limits of probable error. It is 
only when the data are taken as a whole that it is possible to judge of 
the correctness of the general conclusion that within fairly wide limits 
of additional injury there is certainly no decrease in rate of regeneration 
but rather a tendency toward an increase. 
Additional data on these points have been obtained and a further 
analysis of the problem was made with a view to the determination of 
the effect of additional injury to a like organ as compared with addi- 
tional injury to an unlike organ. 
Two of the six experiments will be mentioned here. In the first the 
experiment consisted in the determination of the length of the regener- 
ating right fore-leg of the salamander, Amblystoma punctatum, under 
three degrees of injury; (1) when the right fore-leg alone is removed, 
(2) when its mate is also removed, and (3) when its mate and one-half 
of the tail are removed. The second degree involves the removal of 
additional material of the same kind and the third a further removal 
of material of a different kind. In every case it is the regeneration 
of the fore-leg that is used as the basis of comparison. 
At two days the average regenerated lengths of the fore-leg are re- 
spectively 0.13, 0.16 and 0.15 mm. for the three degrees of additional 
injury; at four days the corresponding values are 0.22, 0.36 and 0.29; 
at six days 0.42, 0.53 and 0.55; at eight days 0.66, 0.83 and 0.73; 
at ten days 0.91, 1.34 and 1.24; at twelve days 1.48, 1.60 and 1.61; 
at fourteen days 1.98, 2.19 and 2.29; at sixteen days 3.02, 3.01 and 
3.08; and at nineteen days 3.84, 3.64 and 3.90. In no case does the 
removed fore-leg with no additional injury to the animal give the high- 
est value for regeneration. In all but two of the cases it has the lowest 
value. 
The comparisons show that the regeneration of a fore-leg is not as 
rapid as when the individual is regenerating no other part of the body 
as it is when the other fore -leg is being regenerated at the same time. 
There is, however, no essential difference between the effect of addi- 
tional injury of a fore-leg and an additional injury of a fore-leg plus one- 
half of the tail. It may be that the effect of additional removal is con- 
fined to removal of a similar part. On the other hand, the accelerating 
effect may be found only within certain degrees of injury, the limit 
being exceeded by the highest of the three degrees. 
