ELECTRICAL CHANGES IN MUSCLE 



261 



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. 90, which represent the 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 77^- 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 direc- 

 tion, but that a change in one direction at one electrode dies away and is succeeded 

 by a similar change in the same direction, which also dies away, at the second 



FIG. 90. Monophasic variations of an injured sartorius. A, at 18 C ; 

 B, at 8 C. (KEITH LUCAS.) 



electrode : that is to say, a diphasic variation implies the progression of a wave 

 of electrical change between the leading-off points. 



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 well as from the mammalian heart 

 is due to the twisting and alteration in direction of the fibres and 

 of the course of the contraction wave which have occurred in the 

 evolution of the heart from a simple tube. The question will te 

 discussed more fully in chapter xiii. 



