40 EXPERIMENTAL PHYSIOLOGY. 



stimulated, whether it be the motor end plate or one end of the 

 fibre in contact with stimulating electrodes. All other parts of 

 the muscle are positive in relation to this wave. Suppose as in 

 Fig. 12 the galvanometer G is connected to the muscle at 2 and 

 3 and the stimulating electrodes are at 1. A single contraction is 

 initiated at 1. This contraction is preceded by a negative electrical 

 condition which first reaches 2 (A), at that moment 2 will be 

 negative in relation to 3, causing a deflection of the galvanometer. 

 The wave continues to move onward, quickly passing 2 and soon 

 reaching 3. When 3 is reached (B) it will become negative to 2. 

 There will therefore be a reversal of the galvanometer. The gal- 

 vanometer moves first in one direction and then in the other. This 

 is called a diphasic variation. The electrical change attending the 

 contraction of muscle is designated the ACTION CURRENT. 



When a muscle is cut or injured, that particular region becomes 

 electronegative to other parts of the muscle which are uninjured. 

 If connected by a conductor a slight current will be set up, called 



the CURRENT OF INJURY. 



FIG. 12. Diagram to show the passage of an electrical change over muscle. When 

 a muscle is stimulated at one end (i) a negative electrical change is started, passing 

 along the muscle, just preceding the contraction. A galvanometer (G) is connected 

 with the muscle by two leading off electrodes, 2 and 3. As the negative change reaches 

 2 (A) the current will pass through the galvanometer from 3 to 2. But when the 

 negative variation reaches 3 (B) the current is reversed. This is called the diphasic 

 variation. 



THE NERVE-MUSCLE AS A RHEOSCOPE. 



The electrical changes set up in muscle can be detected by a 

 vigorous nerve-muscle preparation. The nerve is permitted to 

 touch the muscle at a negative region and a positive region. In 

 a freshly cut muscle at the time of making the second contact, 

 the rheoscopic muscle will twitch. In a muscle stimulated through 

 its nerve the rheoscopic muscle will twitch at each twitch of the 



