138 GENERAL PROPERTIES OF LIVING TISSUES 



a short time. Careful observation shows that 

 in Pararnecium the galvanic reaction consists in 

 placing the long axis of the body in the current 

 lines. The outermost individuals in the liquid 

 will therefore describe a curve corresponding to 

 the curved outer current lines. 



All protozoa and many other animals (for ex- 

 ample, the tadpole and the crayfish) show gal- 

 vanotropism, but in some, movement on closure 

 is toward the positive pole (positive galvano- 

 tropism). 



These experiments on skeletal, smooth, and 

 cardiac muscle, on nerve, and on infusoria, sug- 

 gest that polar excitation occurs wherever a gal- 

 vanic current passes through irritable tissue. 

 Further experience would confirm this view. We 

 have seen that the changes at the cathode when 

 the current is made are not momentary, as re- 

 quired by the hypothesis of DuBois-Keymond, 

 but continue so long as the current flows. This 

 fact appears still more clearly when the influence 

 of the duration of the current is examined. 



INFLUENCE OF DURATION OF STIMULUS 



1. Smoke a drum. Arrange a muscle lever to 

 write on the smoked paper. Prepare non-polariz- 

 able electrodes and fasten them on the glass plate 



