CH. XII.] THE DIPHASIC VARIATION 141 



negative as meaning electro-positive and electro-negative respectively, and as Dr 

 Waller has pointed out, it is time that physiologists adopted the same nomenclature. 

 In what now follows, I propose to adopt Dr Waller's suggestion. 



There is no doubt about the facts as described by Du Bois 

 Keymond. We now adopt, however, an entirely different view of 

 their meaning : in causing this revolution of ideas the principal part 

 has been played by Hermann. Hermann showed that the so-called 

 current of rest does not exist*; it is really a current produced by 

 injury, and is now generally called a demarcation current : the more 

 the ends of the muscle are injured the more positive they become ; 

 and when they are connected to the uninjured centre, a current 

 naturally is set up as described by Du Bois Eeymond. If a muscle 

 is at rest and absolutely 

 uninjured it is iso-electric ; 

 that is, it gives no current at 

 all when two parts of it are 

 connected together by a wire. 



Since Du Bois Rey- 

 mond's researches, the elec- 

 trical changes which occur 

 during a single twitch have 

 been studied also, and before 

 we can understand the " neg- 

 ative variation" of tetanus, 

 it is obviously necessary to Fir 



consider the electrical varia- 

 tion which takes place during a twitch, for tetanus is made up of a 

 fused series of twitches. 



The electrical change during a twitch is called a diphasic 

 variation. The contracting part of a muscle becomes first more 

 positive than it was before ; it then rapidly returns to its previously 

 negative condition. The increase of positivity indicates a disturb- 

 ance of the stability of the tissue ; the disappearance of this increased 

 positivity is the result of a return of the muscular tissue to a state of 

 rest. If the muscle is stimulated at one end, a wave of contraction 

 travels along it to the other end. This muscle-wave (see p. 118) may 

 be most readily studied in a curarised muscle, that is, in a muscle 

 which is physiologically nerveless. The electrical variation travels 

 at the same rate as the visible contraction, but precedes it. 



Suppose two points (p) and (d) of the muscle are connected by 

 non-polarisable electrodes to a galvanometer, and that the muscle- 

 wave is started by a single stimulus applied at A ; as soon as the 

 wave reaches (p) this point becomes positive to (d), and therefore a 

 current flows from (d) to (p) through the galvanometer (G). A 

 moment later the two points are equi-potential and no current flows ; 



