THE TISSUES 65 



YI. Electrical Changes. 



When a muscle contracts certain electrical changes occur. 

 These may be best studied in the heart, which is a muscle 

 which can be exposed without injury. With other muscles 

 the injury inflicted 

 in isolating them sets 

 up electrical currents 

 of injury (p. 45). 



If one end of a wire (f / \\ 



be brought in con- 

 tact with the base of 

 the ventricle by means 

 of a non-polarisable 



electrode (in which FIG. 29. To show electric current of action in a 

 SOme material which muscle (a) compared with that in a galvanic 



J *-"U rt cel1 ( b )' Tne contracting part of the muscle 



does not act upon the is sh ^ ded (g] Galvanometer . 

 muscle and is not 



acted upon by the muscle is in contact with it), and another 

 wire be similarly connected with the apex, and if these 

 wires are led off round a galvanometer, it will be found 

 that with each contraction of the heart an electric current 

 is set up, the one part of the heart becoming first positive 

 and then negative to the other part. 



This means that, when the contraction occurs, the part 

 which first contracts becomes of a higher electric potential 

 than the rest of the muscle, so that electricity flows from 

 it to the uncontracted part in the organ, and from the 

 uncontracting part to the contracting part in the wire round 

 the galvanometer. The contracting part is thus similar to 

 the positive element of a battery, the zinc, the uncontracting 

 part to the negative element, and the wire coming from the 

 contracting part will, therefore, correspond to the negative 

 pole that from the uncontracting part to the positive pole. 



It has now been shown that this current of action occurs 

 along with, and does not precede, the period of contraction. 

 The electric change in contracting muscle may be demon- 

 strated by laying the nerve of a muscle nerve preparation 

 over the muscle of another muscle nerve preparation or over 



5 



