THE TROPISM THEORY OF JACQUES LOEB 353 



line of thought, not to be answered by argument, mutatis mu- 

 tandis to be applied to every kind of tropism. 



That a quick and precise reaction always takes place even 

 in the reversed symmetrical position, as every experiment proves, 

 can be only explained by the fact that the organism as a whole 

 is sensitive to the unusual position and reacts to it. On no 

 account can the reaction be explained by the opposed actions 

 of the two body ht*//es, for such actions would mutually destroy 

 each other. This is the most generally valid argument that 

 can be brought against the tropism theory and it applies to all 

 existing tropisms. The reaction which always may be observed 

 with the reversed symmetrical position cannot be explained by 

 any reflex mechanism, at least, very complicated hypothetical 

 assumptions would have to be made; it shows clearly that even 

 in the lower animals there are voluntary actions which take 

 place as a result of unpleasant sensations, or whatever one may 

 please to call them. 



THE IMPOSSIBILITY OF EXPLAINING THE HARMONIOUS COORDI- 

 NATION OF THE MOVEMENT OF THE TWO BODY HALVES 



The argument just presented, that the reaction of the animal 

 does not depend upon the independent action of the two body 

 halves but represents a harmonious working together of the 

 whole organism, applies, not only to the reversed symmetrical 

 position, but especially to almost every tropic turning around 

 the vertical axis. If such a movement took place in accordance 

 with the scheme of the tropism theory, it might be compared 

 with a row boat containing two men, one pulling the right oar, 

 one the left. If one pulls better or harder than the other, the 

 involuntary result is that the boat begins to turn. Both sides 

 act without coordination and the turning is caused by the differ- 

 ence of the opposing forces of the two sides. This case corre- 

 sponds exactly with the tropism theory, and is exemplified even 

 to the minutest detail in galvanotropism. 



But there is another possibility for turning the row boat. 

 Should the oarsmen intend to turn around, then one of them 

 must row harder than before, while the other will either reverse 

 his stroke to help his partner, or row gently so as not to hinder 

 him. This result is also a turning, but it is caused by the co- 

 ordinated purposeful working together of the two sides; in the 



