ELECTRICAL PHENOMENA 179 



Character of the Electrical Variations in Muscle. 



The existence of electrical currents in tissues did not find 

 direct proof until the year 1824, when Nobili de\ ised the galvano- 

 meter and showed that " natural currents " occur in the frog. 

 Other investigators examined this current of rest and found that 

 in a muscle removed from the body the current in the muscle 

 passed from the ends to the middle and in the external (galvano- 

 meter) circuit from the middle to the ends. It has been conclu- 

 sively proved that these " natiu-al " currents are not natural 

 at all but arc an indication of injury to the muscle. Slight injury 

 is unavoidable in the process of removing the muscle from the 

 body — the less the preparation is injured the smaller is the current 

 obtained from it. In other words, normal resting muscle is iso- 

 electric and therejore currentless (Fig. 38). 



Current of Injury or Demarcation Current. 



The injured part of a muscle is like the injured part of any 

 cell (p. 152 and Fig. 38), " zincative " or electropositive to the 

 uninjured part. That is, if non-polarisable electrodes are led off 

 from injured and non-injured parts to a current-detecting device, 

 it will indicate a passage of current from the uninjured to the 

 injured parts of the preparation through the galvanometer. Within 

 the tissue, of course, the circuit will be completed by the passage of 

 the current from injured to uninjured. This difference of electro- 

 motive force may be demonstrated without a galvanometer. If 

 the nerve from an uninjured muscle be laid over an injured muscle 

 in such a way that at one point it touches a cut portion, then, the 

 undamaged muscle will contract every time the circuit is com- 

 pleted by laying a second point of the nerve on an uninjured 

 portion of the injured muscle. 



This difference in E.M.F. persists as long as the injury. In a 

 degenerating muscle its degenerating portion is electropositive, 

 galvanometrically negative or " zincative " to its normal portion. 

 Naturally, the difference ceases when degeneration is complete. 

 The whole mass is then isoelectric. The current is due, as has 

 previously been explained (p. 153), to physico-chemical differences 

 at the junction of living and dying tissue. Dead tissue gi\'es no 

 current. 



Current of Action (Fig. 43). 



Similar physico-chemical changes are answerable for the wave 

 of " negativity " which precedes the mechanical change in a 

 contracting nuiscle. The part which is just about to contract 

 is electropositive, or " zincative," to the rest. Consider for a 



