MUSCLE 



213 



By applying one non-polarisable electrode to the base 

 and the other to the apex, and leading off round a galvano- 

 meter, it is found — 1st, that, when the heart is at rest, it is 

 of equal electrical potential throughout, and that no current 

 passes round the galvanometer ; 2nd, that, with each 

 contraction of the ventricle, an electric current is set up, the 

 base, where the contraction begins, first becoming " zincy " to 

 the apex, and later the apex, which contracts later, becoming 

 " zincy " to the base. There is a diphasic variation. 



This means that, when the contraction occurs, the part 

 which first contracts becomes of a higher electric potential 

 (more " zincy ") than the rest of the muscle. The contract- 



a 



Fig. 106. — To show electric current of action in a muscle {a) compared with 

 that in a galvanic cell {h). The contracting part of the muscle is 

 shaded, (g) Galvanometer. 



ing part is thus similar to the positive element of a battery — 

 the zinc — the uncontracting part to the negative element. 

 The wire coming from the contracting part will therefore 

 correspond to the negative }Jole — that from the uncontracting 

 part to the positive pole. This current of action precedes 

 the period of contraction. 



When a muscle, in which the current of injury exists, is 

 stimulated, the contracting part becomes electrically more 

 like the injured part ; thus the difference of electric potential 

 is decreased, and a negative variation of the current of 

 injury occurs. 



The electric variations may be demonstrated by laying 

 the nerve of one muscle-nerve preparation over the muscle of 

 another muscle-nerve preparation, or over the beating heart, 



