50 The Mechanistic Conception of Life 



Galvanotropism illustrates this fact in a striking manner. 

 If a galvanic current is passed through a trough filled Tvith 

 water, and animals are placed in this trough, it can be observed 

 that an orientation in relation to the direction of the current 

 takes place in many of the animals, and that they move in the 

 direction either of the positive or of the negative current. 

 This phenomenon we call galvanotropism. In galvanotropism 

 the current lines or the current curves play the same role as the 

 light rays in heliotropism. At those points where the current 

 curves enter the cells^ a collection of ions takes place which 

 influences the chemical reactions. The number of species 

 which show typical galvanotropic reactions is not so great as the 

 number of those showing typical heliotropism. In my opinion 

 this difference is the result of the physical difference in the action 

 of light and of the electric current. Light acts essentially 

 upon the free surface of the animal, while the electric current 

 affects all the cells and nerves. Thus the action of the current 

 upon the skin becomes complicated and modified by its simul- 

 taneous effect upon the nerve branches and upon the central 

 nervous system. The result is thus much more complicated 

 than that of the action of light where essentially only the effect 

 upon the skin and retina is involved. For this reason, a dis- 

 tinct galvanotropism is found more often in organisms with 

 a simple structure, as, for instance, in unicellular organisms, 

 than in vertebrates, although it is also demonstrable in the 

 latter. 



Galvanotropism is, however, purely a laboratory product. 

 With the exception of a few individuals, which have in recent 

 years fallen into the hands of physiologists who happened to be 

 working on galvanotropism, no animal has ever had the chance 

 to come under the influence of an electric current. And yet 

 galvanotropism is a remarkably common reaction among 

 animals. A more direct contradiction of the view that the 



1 Or where the movement of the ions withm the cell is retarded. 



