144 THE ELECTRICAL PHENOMENA OF MUSCLE [CH. XII. 



to uninjured muscle the problem is not so easy. It is at first sight 

 difficult to see why the summed effects of a series of diphasic varia- 

 tions should take the direction of the first phase, as was found to be 

 the case by Du Bois Eeymond in experiments with the frog's gastroc- 

 nemius. One would have anticipated that " negative " variation in 

 the arithmetical sense would be absent altogether, and this is the case 

 in absolutely normal muscles; Hermann has shown that it is so 

 during tetanus of the human forearm. But a muscle removed from 

 an animal's body cannot be considered absolutely normal, and if the 

 two contacts be placed on the comparatively uninjured longitudinal 

 surface, as in fig. 171, a negative variation is observed, each excitatory 

 phase becoming weaker as it progresses, arid the second phase of 

 each diphasic effect is weaker than the first. The following figure 

 illustrates the record obtained by the capillary electrometer from an 



Fio. 175. Electrometer record of injured sartorius during tetanus. (Burdon Sanderson.) 



injured sartorius excited 14 times a second; each oscillation repre- 

 sents a single monophasic variation. The individual oscillations can, 

 however, be seen when the excitations follow one another more 

 rapidly, even up to 80 or 100 per second. 



Muscle is not the only tissue which exhibits electrical phenomena. 

 A nerve which is uninjured is iso-electric ; injury causes a demar- 

 cation current ; activity is accompanied with a similar diphasic wave 

 travelling along the nerve simultaneously with the nervous impulse. 

 The activity of secreting glands, vegetable tissues, retina, etc., is 

 accompanied with somewhat similar electrical changes, which we 

 shall study in detail later. 



But the most prominent exhibition of animal electricity is seen 

 in the electric organs of electric fishes. In some of these fishes the 

 electric organ is modified muscle, in which a series, as it were, of 

 hypertrophied end-plates correspond to the plates in a voltaic pile. 

 In other fishes the electric organ is composed of modified skin glands. 



