MUSCLES AND PHENOMENA OF CONTRACTION. 133 



called the muscle currents. They have, however, probably 

 no real physiological significance, because it has been found 

 in many different fields that a tissue which is injured and 

 dying becomes electrically negative to tissues left unhurt. 

 As the muscle where it was cut at the ends has begun to 

 die, these ends have become negative with reference to the 

 central unhurt portion. For this reason when connections 

 are made currents circulate. These currents are, conse- 

 quently, not found in living muscle, because in this latter 

 case there are no dying portions to be negative. 



WAVE OF NEGATIVE VARIATION. 



If now, such a cut-out muscle be connected with the 

 galvanometer, and the presence of the current circulating 

 through it indicated by the rotation of the magnetic needle, 

 and if while this is going on, the muscle be stimulated to 

 contraction, it is found that during the latent period the 

 needle tends to swing back to its original position. This 

 indicates that during this latent period there must have 

 been set up in the muscle substance currents of electricity 

 which run counter to the first currents, and so neutralize 

 them to some extent, causing the needle to swing back 

 toward its resting point. This current is called the wave of 

 negative variation. This wave is explained on grounds sim- 

 ilar to that of the ordinary muscle currents. The muscle 

 substance not only when dying, but also when stimulated, 

 becomes negative at such points. As the nerve enters the 

 muscle near the middle, and as, therefore, the point of 

 stimulation arises here, this becomes negative toward the 

 ends of the fibres which the stimulus has not yet reached. 

 Thus there will be set up counter currents tending to run 

 from the more positive ends to the negative middle. But 

 as these run in exactly the opposite direction to the cur- 

 rents caused by the dying negative ends, they tend to neu- 

 tralize each other more or less, and so the needle swings 

 back toward the resting point. 



