THE PHYSIOLOGY OF REGENERATION 347 



We thus discover that also in the case of the salamander the per 

 cent of water in the regenerating tissue increases rapidly at first 

 (89.08 per cent), then decreases again, tending towards the normal 

 (82.08 per cent). Although these observations are not enough to 

 trace in fullness the changes in the water content of the re- 

 generated tails of Diemyctylus, yet they suffice to substantiate 

 the former results on Podarke as well as to throw light upon 

 some points which remained obscure in those experiments. 



SUMMARY 



As the curve of formative growth and that of posterior regenera- 

 tion are essentially alike in their important characteristics, it 

 seemed desirable to investigate the question whether the factors 

 in the two processes are also similar. Numerous experiments on 

 both plants and animals have demonstrated the fact that in 

 formative growth the per cent of water rises to a maximum during 

 the period of rapid growth, and then falls as the organism ap- 

 proaches the adult condition. With this in view, I have studied 

 the water content at successive stages of regeneration in a poly- 

 chaet — ^Podarke obscura. The result is practically the same as in 

 formative growth ; soon after an operation the water content rapidly 

 rises, reaching a maximum approximately between the first and 

 second weeks; subsequently, it begins to decline. As it was found, 

 furthermore, that the period of maximum water content and the 

 period of maximum regenerative activity approximately coincide, 

 as in formative growth, the similarity between growth and regen- 

 eration was thereby shown to be still greater. Close analysis, 

 however, revealed that, while from the point of view of the end 

 result {i.e., the rise and fall of the curve of the per cent of water) 

 growth and regeneration are alike, the two processes involve dis- 

 similar factors. In formative growth the increase in size and in 

 the per cent of water are brought about through imbibition of 

 water from the surrounding medium; in regeneration this does 

 not seem to be the case, as is shown by a comparison of the abso- 

 lute quantities of water and of dry substance at various stages. 

 The regenerating animals, whether fed or starved, lose in weight 



