PHYSICO-CHEMICAL BASIS OF TRANSMISSION 393 



missions between neurones in the central nervous 

 system and between nerve-endings and muscle cells 

 are evidently by contact. Such transmissions point 

 almost certainly to electrical conditions. The sensitivity 

 of certain irritable elements to electrical currents in the 

 surroundings has in some cases been developed to a 

 remarkable degree; for example, the catfish will respond 

 to the dipping of a metallic rod into the aquarium at a 

 distance of several centimeters from the fish.^ It is 

 possible that such animals may detect Hving prey 

 through the action-currents accompanying muscular 

 movements. 



Transmission of excitation or other physiological 

 influence — implying transmission of chemical influence 

 to a distance in protoplasm — may be called "physi- 

 ological distance-action," after the analogy of ''chemical 

 distance-action"; the latter is an electrical phenomenon 

 depending on the mutual influence of the. electrode 

 areas in circuits.^ A simple example will illustrate.^ 

 When a copper or platinum wire, e.g., 25 centimeters 

 long, is immersed in a vessel of dilute H2SO4 and touched 

 at one point with a piece of zinc, instantly bubbles of 

 hydrogen start out from the surface of the wire along 

 its entire length. The zinc forms the anode in the local 

 circuit produced by the contact, the copper or platinum 

 is the cathode, hence hydrogen is formed from the surface 

 of the latter at all points where the current-intensity is 



^ Parker and von Heusen, American Journal of Physiology, XLIV 

 (1917), 405 



^'Cf. Ostwald, "Chemische Fernewirkung," Z. physik. Chem., IX 

 (1891), 540. 



3 For other similar instances and a fuller discussion of the biological 

 analogies cf. Biological Bulletin, XXXIII (1917), i35; cf. pp. 157 ff. 



