CH. XI.] 



THE ELECTROMETER RECORD 



125 



the uninjured surface and the other on the cut end (see fig. 143), the 

 electrical response is a different one. 



Under these circumstances, the electrical change is a monophasic 

 variation, for when the muscle-wave reaches d, this part of the 

 muscle, owing to its injured state, does not respond to the 

 excitatory condition, and the electrical re- 

 sponse is also extinguished. 



The grey curve in figs. 142 and 144 is the 

 graphic record of the change as revealed by 

 the capillary electrometer. It will be seen 

 that the ascending limb of the curve is iden- 

 tical in the two cases, but that the second 

 phase is absent. From the point at which the 

 diphasic curve approaches its culmination the 

 injury curve diverges from it, continuing to 

 ascend; the line soon after becomes hori- 

 zontal, and then begins slowly to decline. 

 This long tail denotes only the gradual dis- 

 appearance of polarisation of the mercury 

 meniscus. 



The meaning of such photographic records be- 

 comes clear by testing the electrometer with known 

 differences of potential, and from such data it is 

 possible to construct what may be called an interpre- 

 tation diagram (fig. 144). The horizontal line is that 

 of equipotentiality of the two surfaces of contact p 

 and d. The curve P' expresses the relative positivity 

 of the surface p ; the curve D', the corresponding 

 relative positivity of the surface d. S' is a curve 

 of which the ordinates are the algebraic sums of the 

 corresponding ordinates of P' and D'. S is the 

 photographic curve which expresses S' ; P is the 

 photographic curve which expresses P' (monophasic 

 variation). The numbers under the horizontal line 

 indicate hundredths of a second ; the distance t t' 

 expresses the time taken by the wave in its progress 

 from p to d. 



From these considerations we can now pass to study what occurs 

 when the muscle enters into tetanus. The simplest case is that which 

 was first observed by Du Bois Eeymond. He placed his non- 

 polarisable electrodes in the positions indicated in fig. 143, one (p) 

 on the comparatively uninjured surface, the other (d) on the devital- 

 ised cut end. He sent in the tetanising series of shocks at A. The 

 electrical response is under these circumstances a summation of the 

 individual electrical responses evoked by instantaneous stimuli ; and 

 the monophasic character of the single response explains easily what 

 occurs during tetanus ; the centre of the muscle becomes more 

 positive than it was before, and so the electrical difference of potential 



FIG. 144. Interpretation dia- 

 gram . (Burden Sanderson . ) 



