PREFACE vii 



phenomenon, leaving no necessity nor room for the postiilation 

 of a guiding principle aside from the purely physico-chemical 

 forces. 



The writer has confined himself to experiments on one form 

 only, which, however, is unusually favorable for quantitative work 

 on regeneration. The reason for this restriction lay in the fact 

 that it was his intention to find a rationalistic law which could 

 be used as a guide in further experiments on regeneration. For 

 this purpose it was essential to confine himself in the beginning 

 to the elaboration of this law in an organism which permitted 

 the carrying out of the necessary quantitative experiments, and 

 BryophyUum met this prerequisite. We are already in possession 

 of an enormous number of enigmatic though often interesting 

 observations on regeneration in different animals and plants, and 

 it seemed of little value to add to this store of riddles. It is 

 primarily not more facts which are needed in this field but a 

 method and a principle which allow us to pass from the stage of 

 blind empiricism to the stage of an oriented search. As long as 

 the investigation of a natural phenomenon is in the stage of 

 blind empiricism we never know what to look for in our experi- 

 ments nor what to measure, and we are not able to judge whether 

 we are on the road to progress or whether we are losing ourselves 

 in a jungle of futile experiments. With a rationalistic law and 

 a rationalistic method as guides, this danger is avoided. The 

 writer believes that the mass relation referred to can render this 

 service in the field of regeneration, and that the extremely simple 

 method of correlating the dry weight of regenerated organs with 

 the dry weight of the regenerating plant serves as a sufficiently 

 safe method for a first approximation to exact results and 

 conclusions. 



The contents of the book is divided into two parts, the first 

 correlating mutilation and regeneration on the basis of the mass 

 relation, and the second making an attempt at a similar treatment 

 of the problem of the polar character of regeneration. 



The book is based on a number of papers published in the 

 Journal of General Physiology, but it seemed advisable to put the 

 main results into the form of a short monograph where the facts 

 could be arranged in a more logical sequence than was possible 

 in the original publications. The main experiments required 

 for the proof of the theory were once more repeated before the 

 book was written and in many cases these experiments were 



