232 



PHYSIOLOGY 



FIG. 88. Superimposed photographs of 



tion of the sartorius in response to a single stimulus. 

 (BURDON SANDERSON.) 



at any spot lasts only about -^ second, and there is not a prolonged equipotential 

 period, as in the case of the heart. The nature of the variation is, however, obvious, if 

 we compare the electrometer record of an intact and therefore currentless muscle with 

 that of a muscle in which one of the leading-off points has been injured, so as to give 

 rise to a demarcation current. The two curves are given in Fig. 88, the upper shadowy 

 tracing being that obtained from the injured muscle. It will be seen that the dis- 

 tinguishing character of 

 an electrometer record of 

 a diphasic variation in 

 the rapidly contracting 

 striated muscle consists 

 in the fact that the down- 

 stroke of the image of 

 the meniscus is as rapid 

 as the upstroke, whereas 



the "electrical varia- the monophasic variation 

 of the injured muscle 

 presents a slow fall pro- 

 duced by the gradual 



leakage of the charge imparted to the instrument back through theelectrodes and muscle. 

 When such a record is analysed, we obtain a curve similar to those in Fig. 89, which repre- 

 sent monophasic variations of a sartorius injured at one end, under different conditions of 

 temperature. A similar curve to the diphasic variation can be obtained by putting 

 in a current of similar E.M.F. from a battery, first in one direction for ^^ second, and 

 then in a reverse direction 

 for another ^^ second. It 

 must be remembered that 

 a diphasic variation does not 

 mean that one part of a 

 muscle changes from normal 

 in one direction, and then 

 swings back past the normal 

 in another direction, but 

 that a change in one direc- 

 tion at one electrode dies 

 away and is succeeded by a 

 similar change in the same 

 direction, which also dies 

 away, at the second electrode : 

 that is to say, a diphasic 

 variation implies the pro- 

 gression of a wave of electrical 

 change between the leading- 

 off points. Using a string 

 galvanometer, which reacts 

 much more rapidly, the 

 diphasic nature of the varia- 

 tion is immediately apparent 

 from the photographic record, 

 even with voluntary muscle, FIG. 89. Monophasic variations of an injured sartorius. 



or nerve< 



A, at 18 C. ; B, at 8 C. (KEITH LUCAS.) 



The electrical variation obtained by leading off a heart beating normally 

 is a much more complex affair, and even now physiologists are not agreed as 

 to its interpretation. Gotch has suggested that the complex character of 

 the variations obtained both from the spontaneously beating frog's heart as 



