TROPISMS AND RELATED PHENOMENA 145 



development of energy now predominate in those muscles which move 

 the swimming appendages forward. In this way the animal can 

 swim backward easily, while it is difficult or impossible for it to swim 

 forward. 



"PalcBmonetes can also walk sidewise. This movement is pro- 

 duced by the pulUng of the legs on the side toward which the animal 

 is moving (contraction of the flexors), while the legs of the other side 

 push (contraction of the extensors). If a current be sent transversely, 

 say from right to left, through the animal, the legs of the right side 

 assume the flexor position, those of the left side the extensor position. 

 The transverse current assists the animal in moving toward the right, 

 toward the anode, and prevents it from moving toward the left, toward 

 the cathode." * 



The galvanotropic reactions were first discovered in vertebrates. 

 Purkinje noticed that if a galvanic current is sent through the brain 

 of a human being, sensations of motion and dizziness are produced. 

 Brenner recognized the polar character of this effect, and found that 

 if a current of sufficient intensity is sent laterally through the head, 

 the person falls toward the anode side upon making the current, toward 

 the cathode side, upon breaking the current. Mach noticed that if a 

 current is sent sidewise through fishes, the animals have a tendency 

 to roll toward the anode side.f 



The introduction of the term "galvanotropism" into physiology dates 

 from J. Miiller-Hettlingen, who found in Hermann's laboratory that 

 if the seedlings of Vicia faba are exposed to a constant current, the tips 

 of the roots bend toward the cathode. J Hermann soon afterward 

 made similar experiments on the larvae of frogs. He found that these 

 animals, when put into a trough through which a current goes, are turned 

 into the direction of the current curves, putting their heads toward the 

 anode. § I must, however, admit that I never succeeded in repeating 

 this experiment on tadpoles. 



Blasius and Schweizer|| found that a large number of animals, when 

 put into a trough with water through which a constant current goes, 

 have a tendency to go to the anode. They assume that the current 

 acting upon the central nervous system causes sensations of pain when 

 it goes in the ascending direction through the animal; while it calms 

 the animal when it goes in the opposite direction (from head to tail). 



* Quoted from Loeb, Comparative Physiology of the Brain and Comparative Psychology, 

 New York, 1900. 



t Mach, Grundlinien der I.ehre von den Bewegungsempfindungen, Leipzig, 1875. 

 i J. Muller-Hettlingen, PflUger's Arckiv, Vol. 31, p. 193, 1883. 

 § Hermann, PfiUger's Archiv, Vol. 37, p. 457, 1885 ; and Vol. 39, p. 414, 1886. 

 II Blasius und Schweizer, Pfluger's Archiv, Vol. 53, p. 493, 1893. 



