ELECTRICAL CHANGES IN MUSCLE 2 25 



the ends to the middle, and in the external circuit from the middle (or equator) 

 to the ends. It was formerly thought that this current was always present 

 in all normal muscles, and it was spoken of as the ' natural muscle current ' 

 the muscle was said to be made up of a series of electromotive molecules, the 

 equator of each molecule being positive to the two poles (du Bois Raymond). 

 It has been conclusively shown, however (by Hermann and others), that this 



Z/7 



+ 



Zn 



SO* CL 



a 



Zn 



+ 



FIG. 77. 



FIG. 78. Current of rest. 



current of resting muscle is not a natural current at all, but is due to the 

 effects of injury in making the preparation. The less the preparation is 

 injured, the smaller is the current to be obtained from it, and in some con- 

 tractile tissues, such as the heart, there may be absolutely no current during 

 quiescence. 



Hermann describes the fact of the existence of currents of rest thus : 

 " In partially injured muscles every point of the injured part is negative 

 towards the points of the uninjured surface." Fig. 78 shows the direction 



of the current in a muscle with two cut ends , 



When the whole muscle is quite dead, this cur- fa * * * + * * * 

 rent of rest, or ' demarcation current ' (Her- ; i * 



mann), disappears. The current is due to the ^ *~^ " 



electrical differences at the junction of living 

 and dying (not dead) tissue. If the sartorius 

 of the frog be cut out and immersed for twenty- 

 four hours in 0-6 per cent. NaCl solution made with tap water (i.e. con- 

 taining lime), all the injured fibres die, and the uninjured fibres are then 

 found to be iso- electric and therefore currentless. 



The existence of this current may be demonstrated without using a galva- 

 nometer. If the nerve of a sensitive muscle-nerve preparation (a, Fig. 80) be 

 allowed to fall on an excised muscle 6, so that twp 

 points of the nerve are in contact with the cut end 

 and with the surface of the second muscle 6, the 

 muscle a will contract each time the nerve touches b 

 so as to complete the circuit. 



Whatever be the explanation of "this curreni 

 resting muscle, there is no doubt that a very definite 

 electrical change occurs in a muscle when it contracts 

 To show this change, we may lead off two poi 

 on the cut end and one on the surface of the muscle of a muscle 

 paration, to a galvanometer. We shall then obtain a deflecti 



FIG. 79. 

 Rheoscopic frog. 



