232 



PHYSIOLOGY 



muscle or in nerve is also due to a diphasic variation. In this case the electrical change 

 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 uppel 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 



FIG. 88. Superimposed photographs of the electrical varia- the monophasic variation 

 tion of the sartorius in response to a single stimulus, of the injured muscle 

 (BUEDON SANDERSON.) presents a slow fall pro- 



duced by the gradual 



leakage of the charge imparted to the instrument back through the electrodes 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 2^ 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 electri- 

 cal change between the lead- 

 ing-off points. Using a string 

 galvanometer, which reacts 

 much more rapidly, the 

 diphasic nature of the varia- 

 tion is immediately apparent SEC. . oos ., 

 from the photographic record Flo 89j Monophasic variations of an injured sartorius. 

 even with voluntary muscle, A , at 18C. ; B, at 8C. (KEITH LUCAS.) 

 or nerve. 



The electrical variation obtained by leading off a heart beating normally 

 is a much more complex affair. The question will be discussed more fully 

 in chapter xiii. 



