ELECTROTONTTS. 117 



The phenomena of electrotonus are very simple ; and it 

 is only when we attempt to construct a theory to account for 

 these phenomena that the subject becomes obscure. Sup- 

 pose, for example, that a nerve be exposed in a living ani- 

 mal, or in one just killed, and a galvanic current be applied 

 from a Grove's battery, in which about twelve square inches 

 of zinc are exposed to the action of a liquid containing one 

 part of ordinary sulphuric acid to eight of water. 1 A deli- 

 cate galvanometer applied to the nerve either above or be- 

 low the poles will indicate a decided current, much more in- 

 tense than the tranquil nerve-current between the exterior 

 and the cut surface. This electrotonic condition exists so 

 long as the galvanic current is continued ; and, as has been 

 shown by Matteucci in operating upon the higher animals 

 rabbits, dogs, fowls, and sheep when the galvanic current 

 has been sufficiently powerful and prolonged, the electroto- 

 nic condition persists for a certain time after the stimulus 

 has ceased. 3 As we have seen that the muscular contraction 

 following galvanic stimulation of a nerve is powerful in pro- 

 portion to the extent of nerve included between the poles 

 of the battery, so the electrotonic condition increases in 

 intensity with the length of the nerve subjected to the con- 

 stant current ; provided, always, that the strength of the 

 current be slightly increased to compensate the enfeebling 

 action due to the resistance in the increased length of the 

 circuit. 3 



^\Ve do not propose to discuss fully the various theories 

 that have been advanced in explanation of the phenomena 

 of electrotonus. Matteucci has made a series of interesting 

 observations upon conductors formed of very fine wires, one 

 of platinum and the other of amalgamated zinc, covered with 

 cotton thread soaked in a neutral solution of sulphate of 



1 RUTHERFORD, lor. tit. 



8 MATTEUCCI, Origine de Telecirotone des nerfs. Revue des cours stientifique^ 

 Paris, 1867-'68, tome v., p. 279. 



MORGAN, Electro-physiology and Therapeutics, Xew York, 1868, p. 495. 



