THE TISSUES 



machines, such as steitm-engines, muscle must be regarded as 

 an economical worker, and it has the advantage that the 

 heat liberated is necessary to maintain the temperature at 

 which the chemical changes which are the basis of life can 

 go on. 



VI. Electrical Changes in Muscle 



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. 42). 



FIG. 30. To show electric current of action in a muscle (a) compared with that 

 in a galvanic cell (6). The contracting part of the muscle is shaded. 

 (g) Galvanometer. 



If one end of a wire be brought in contact with the base of 

 the ventricle by means of a non-polarisable electrode (in which 

 some material which does nut act upon the 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 galvano- 

 meter. The contracting part is thus similar to the positive 



