CII. XII.] 



THE ELECTROMETER RECORD 



143 



the uninjured surface and the other on the cut end (see fig. 173), 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 response is also extinguished. 



The grey curve in fig. 172 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 identical 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 horizontal, and then begins slowly 

 to decline. This long tail denotes only the 

 gradual disappearance of polarisation of the 

 mercury meniscus. 



The meaning of such photographic records becomes 

 clear by testing the electrometer with known differ- 

 ences of potential, and from such data it is possible to 

 construct what may be called an interpretation dia- 

 gram (fig. 174). The horizontal line is that of equi- 

 potentiality of the two surfaces of contact Q>) 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 correspond- 

 ing 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 (/>) 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. 173, one (p) on the com- 

 paratively uninjured surface, the other (d) on the devitalised cut 

 end. He sent in the tetanising series of shocks at A. The elec- 

 trical 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 

 between the centre and the injured end is lessened. But with regard 



FIG. 174. Interpretation dia- 

 gram. (Burdon Sanderson.) 



