CH. xii.] THE NEGATIVE VARIATION. 151 



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, and 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 injured 

 sartorius excited 1 4 times a second ; each oscillation represents 

 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. 



Fij;. 175. Elfctroinrtcr record <>f injured sartorius during tetanus. (Burdon Sanderson. 



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, and also of the retina, is 

 accompanied with electrical changes of the same kind. 



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. But in each case the electric discharge is 

 the principal phenomenon that accompanies activity. 



In conformity with usage I have retained in the foregoing description of 

 the electrical phenomena in living tissues, the terms positive and negative 

 in the loose and incorrect sense in which they are employed by physiologists. 

 The words negative and positive should really be transposed. In a Daniell 

 cell, the zinc is the positive clement, and is connected to the negative pole. 



