GALVANOTROPISM 33 



assumed that the current, acting upon the central nervous 

 system, causes sensations of pain when it goes in the 

 direction from tail to head in the animal; while it has a 

 soothing or hypnotizing effect when it goes in the opposite 

 direction, namely from head to the tail. In the latter 

 case the head is directed toward the anode. The authors 

 assume that the animals choose the position with least 

 pain, i.e., with their heads to the anode. This assumption 

 is wrong, since we know that when a galvanic current is 

 sent through the head of a human being automatic 

 motions comparable to those observed in animals occur 

 which are not voluntary and which are unaccompanied 

 by any pain sensation. Thus when a galvanic current is 

 sent laterally through the head, the person falls toward 

 the anode side but has no feeling of pain. Mach noticed 

 the same effect of falling to the side of the anode when a 

 galvanic current was sent sidewise through fishes. 330 

 These galvanotropic motions are in reality forced move- 

 ments, and this has been proved by direct observations. 

 It was shown by Loeb and Maxwell 307 in experiments 

 on crustaceans and by Loeb and Garrey 306 on salaman- 

 ders that when we send a galvanic current through ani- 

 mals which go to the anode, changes in the position of 

 the legs occur comparable to the changes in the position 

 of fins and eyes mentioned in the previous chapter, and 

 that these changes are of such a character as to make 

 it easy for the animal to move in the direction of the anode 

 and difficult if not impossible to move in the opposite 

 direction. 



In all these experiments it is of importance to choose 

 the proper density of the current. For the experiments on 

 the shrimp (Palamonetes) 807 the animals were put into a 

 3 



