ANIMAL ELECTRICITY ; 



563 



contraction of both. In this case, the current of action in one muscle 

 excites the other directly (Fig. 300). 



Normally, the presence of such currents is shown by the use of the 

 galvanometer and special apparatus (Fig. 301). 



If an injured muscle be led off to the galvanometer and stimulated, 

 it is found that on each single contraction, or, better still, on tetanus, 

 the current of injury is diminished or may be overbalanced, since 



10cm. 



Fiu. 302. KEITH LTTCAS MOIST CHAMBER AND ELECTRODES. 



A, Glass rod; B, B, tubes containing platinum electrodes; the leading off electrodes 

 are glass tubes filled with Ringer s solution plugged by filter candles containing 

 zinc sulphate and below by cotton-wool wads D, D, connected to muscle ; E, 

 ebonite trough with glass sides enclosed in felt F : O, Ringer's solution immersing 

 lower part of muscle; H, inlet, J, outlet for fluid; A', accessory outlet for totally 

 immersing muscle when J is closed. 



the change from rest to action is greater in the uninjured part than 

 in the injured part. This diminution of the injury current is termed 

 " negative variation " (Fig. 297). 



When uninjured tissue passes into action, there is what is termed 

 a " diphasic variation." This is because first the part proximal to 

 the~stimiilus is active, then the distal part; the action is not simul- 

 taneous throughout the whole of the muscle. When A is active 



