A CRITICISM OF THE TROPISM THEORY OF 



JACQUES LOEB>.* 



W. VON BUDDENBROCK 



Heidelberg University 



CONTENTS 



PAGE 



Introduction 341 



Outline of the arguments 344 



Cases of true tropisms in which the premised conditions are absent 345 



Tropisms without energy rays: geotropism of marine forms 345 



Cases of tropisms which occur in a contradictory manner, although the prem- 

 ised conditions are present 347 



Sidewise movements of crabs 347 



Changeable heliotropism : starfish, Crustacea 348 



The turning around the horizontal cross axis 349 



The reaction from the reversed symmetrical position 352 



The coordinated movement of the two body halves 353 



The impossibility of finding the axis of turning 355 



The disagreement of the tropism theory with the presence of a reflex arc 356 



The purposeful nature of tropisms 361 



Summary and conclusions 364 



INTRODUCTION 



There are two classes of biological investigators. One is con- 

 cerned with facts; the theories which are based upon known 

 facts serve him only to explain facts, to condense them into 

 some general aspect, so that a deeper insight into the meaning 

 of the whole problem may be gained. Even when his work 

 lies along theoretical lines, to him facts are of the first import- 

 ance. Should a fact be discovered which contradicts the theory, 

 then the theory must suffer. 



To the other kind of investigator the insignificant isolated 

 facts are of no importance. His soaring mind desires universal 

 recognition for the results of his achievement. The glittering 

 theory is everything to him, the facts only its servant. If the 

 fact does not suit, then it will be forced into the Procrustean 



1 The literature of the whole subject may be found in Loeb's paper: Die Tro- 

 pismen, in Winterstein's Handbuch der vergl. Physiologie, Bd. 4, 1913. 



2 The original text of this paper is published in the Biol. Centralblatt, Bd. 35, 

 Nr. 11, 1915. 



