ENVIRONMENT AND REGENERATION 465 



the two processes. What is true of the effects of hydrogen ion 

 concentration is also true of the effects of oxygen on regeneration. 

 As yet no experimental studies are known to have been made 

 on regeneration in varying concentrations of oxygen. As rapid 

 oxygen metabolism and rapid growth are often associated, the 

 carbon-dioxide production experiments were undertaken to see 

 whether any correlation could be traced between the rate of 

 regeneration of a part and the oxygen metabolism of the animal 

 as a whole, and whether substances stimulating to oxygen 

 metabolism are, as Whitley supposed, beneficial to the organism. 

 In this work the author has been concerned only with the extrinsic 

 factors of regeneration. The intrinsic factors have been con- 

 sidered only as they arose as necessary corollaries to the work on 

 environmental effects. 



Throughout this paper the word 'regeneration' has been used 

 for those processes of cell multiplication and growth which result 

 in the increase of size of the new part. The author is fully aware 

 that the general term 'regeneration' is commonly used to include 

 three processes: dedifferentiation, growth, and differentiation. 

 In order, however, to avoid the use of the word 'growth,' which 

 would lead to confusion of the processes under experiment with 

 the growth of the organism as a whole, and further to avoid the 

 repeated use of long explanatory clauses, the simple word 'regen- 

 eration' has been used in this restricted sense. 



MATERIALS 



The tadpoles studied were larvae of Rana clamata (Dau) 

 collected from a spring-fed marsh near Muncie, Illinois. Three 

 collection trips were made, dated October 9, 1917, March 5 and 

 24, 1918. This supply was supplemented during the middle of 

 the winter by a few tadpoles purchased from a local dealer. 

 All tadpoles were identified by means of key to larval amphibia, 

 Wright ('14). The stock was kept in a greenhouse in an alberine 

 tank supplied with running water to a depth of about 6 inches. 

 The food supplied was filamentous green algae. All tadpoles 

 were kept fasting during the experiments. 



