STIMULI AND THEIR ACTIONS 



421 



expression, for a muscle completel}' extended cannot be extended 

 further. But that the process at the anode is as is stated above is 

 seen at once when smooth or cross-striated muscles that are parti- 

 ally contracted are stimulated. In such muscles at the moment 

 of making the current a local expansion takes place at the anode. 

 Biedermarm was likewise able to establish upon heart-muscle the 



?^^^^^^ 



Fig. 202. — Pavamcecium aurelia, polar excitation. A, Unstimulated individual. B, Action of a 

 strong current ; the anodic end has become compressed into a point and the contents of the 

 trichocysts have been extruded. C, The positions taken by the cilia (only the outline of the 

 body is sketched) ; at the anode the cilia .are bent more strongly toward the pointed hinder 

 end of the body, at the kathode more towai-d the blunt foi-ward end. D, The same, the 

 position of the body being reversed. (After Ludloff.) 



re\erse fact, that upon breaking, in addition to the excitation of con- 

 traction at the anode, an excitation of expansion takes place at the 

 kathode. It is interesting that the effects at the two poles upon 

 making are the opposite of those upon breaking. The phenomena 

 in the nerve afford a complete analog}' to this. In the nerve also 

 there are opposite effects at the two poles. This is expressed in 

 the change in irritability that manifests itself at the poles when 

 a galvanic current is passed through the nerve. For example, 



