THE RELATION BETWEEN DEGREE OF INJURY AND 
RATE OF REGENERATION—ADDITIONAL OBSER- 
VATIONS AND GENERAL DISCUSSION?! 
CHARLES ZELENY 
In some recent papers? I have given the results of experiments 
which show an increase in rate of regeneration of an organ with 
increase in degree of injury to the individual. ‘This relation does 
not keep up indefinitely but sooner or later an optimum degree 
of injury is reached beyond which additional injury results in a 
decrease in rate. In some cases the optimum is comparatively 
high, in others, comparatively low. 
Realizing the many factors that control rate of regeneration 
and the difficulties encountered in attempting to eliminate all 
but one of them I have extended the experiments with two points 
in view, (1) the more careful control of the accessory factors, 
and (2) the inclusion of as many different forms as possible. 
The new results together with a summary of the old, make up the 
subject matter of the present paper. 
GENERAL METHODS AND SOURCES OF ERROR 
Since in any particular case the rate of regeneration is deter- 
mined by a large number of factors, many of which give marked 
changes in rate with slight changes in the factors, success in 
obtaining the pure effect of degree of injury is dependent upon 
the completeness of elimination of the other factors. ‘The prin- 
cipal method employed was chosen with this point in veiw. It 
consists of a study of the change in rate of regeneration from a 
particular level when other parts of the individual are subjected 
to different degrees of injury. In the present paper by effect of 
1 Contributions from the Zoélogical Laboratory of Indiana University. No. 109. 
2 See Bibliography. 
THE JOURNAL oF EXPERIMENTAL ZOOLOGY, VOL. VII, No. 3. 
