9] RATE OF REGENERATION— ZELENY 



PART I 



THE RATE OF REGENERATION FROM NEW TISSUE COM- 

 PARED WITH THAT FROM OLD TISSUE 



In comparing first and second regenerations from the same level 

 one of the difficulties that presents itself is the impossibility of making 

 the second cut exactly in the path of the first. This is true not only 

 because of the error in manipulation but also because the old and the 

 new tissues become intermingled and do not retain a distinct dividing 

 line. At the cut surface there is old tissue alone, old and new tissue, 

 or new tissue alone according as the second cut comes inside of the first 

 level, exactly at the level, or outside of it. 



The experiments about to be described were devised with a view to 

 the testing of the relative rates from old and from new tissue. Other 

 factors being eliminated, are new cells which are recently produced in 

 a regenerating part able to carry on a repetition of the process more 

 expeditiously than old cells which have not been directly concerned in 

 such a process? 



There has been no selective elimination of data. As in former 

 papers of a similar character all the data obtained by the author on the 

 topic at hand are included. 



Experiment I Series 3628-3675 



Tadpoles of Rana clamitans with an average length of 33.4 

 mm. were used. They were fed just enough to keep them in good 

 condition without much growth. All were collected at one time in a 

 single pool and during the course of the experiment factors apart from 

 the one under investigation were made as nearly alike as possible. This 

 elimination of outside factors was facilitated by subdividing the tad- 

 poles into sets of two each, the two individuals of a set being exactly 

 alike except for the factor under consideration and one being used for 

 regeneration from old tissue and the other for regeneration from new 

 tissue. 



