55* 



ELECTRICAL CURRENTS OF ACTIVE MUSCLE. 



The variation is diphasic 1st phase base negative to apex ; 2nd phase apex negative to base 

 ( Waller). The first phase begins -fa" before the commencement of contraction. 



One of the best objects for this purpose is the contracting heart, which is placed 

 upon the non-polarisable electrodes connected with a sensitive galvanometer. Each 



beat of the heart causes a deflection of the needle, which 

 occurs before the contraction of the cardiac muscle 

 ( K'nlliker and II. Midler). The electrical disturbance 

 in the muscle causing the negative variation always 

 precedes the actual contraction (v. Helmholtz, 1S45). 

 Still it lasts throughout the whole duration of the con- 

 traction (Lee). When the completely uninjured frog's 

 gastrocnemius contracts by stimulating the nerve, 

 there is at first a descending and then an ascending 

 current (Sig. Mayer, 334, II.). 



More exact observations on the electrical processes of the pul- 

 sating heart show that complicated phenomena occur. The apex 

 of the dog's heart is negative to the base during systole. In 

 many cases this is preceded, and in some it is followed, by an 

 opposite condition {FrMerieq), i.e., a diphasic variation. If the 

 heart be arrested in diastole by stimulation of the vagus (369), 

 there is a positive variation of the muscle-current (Gaskell, 

 Fano). Waller has demonstrated a true electrical variation of 

 Frog. (Jastrocnemius led off the human intact heart, 

 to electrometer from the rT - ,- . .. . , ,, . , ,, - 



middle of the muscle and [Heart. Gaskell has shown that, when the vagus of 

 from the tendon. Contrac- a tortoise is stimulated so as to arrest its heart in diastole, 

 tion excited by a single the action of the inhibitory nerve is accompanied by a 

 break induction shock ap- Uive e i ectrica i var iation of the heart-current, while 

 plied to the sciatic nerve. 7 ,. , ,. c , , ., -. / . . 



> ; electrometer vi muscle stimulation of the sympathetic (augmeutor) nerve causes 

 t, time in a 1 7j th sec. (muscle an electrical variation of the same sign as that caused by 

 to H._,S0 4 ; tendoij, to Hg) a contraction in the non-beating tissue of the ventricle 

 of the toad. In both cases, the respective nerves can 

 produce their electrical effect after the heart has been brought to standstill by 

 the application of muscarin to the sinus. These experiments are of the utmost 



Fig. 403. 



Fig. 404. 



Frog's heart. Spontaneous contraction, e, e, electrometer ; h, h, heart's contraction ; t> t, 



time in ^th sec. (apex to H 2 S0 4 , base to Hg) ( Waller). 



importance in connection with the theory of the action of these nerves on the heart 

 ( 370), and the mode of action of poisons on the heart itself.] 



Secondary Contraction. A nerve-muscle preparation may be used to demonstrate 

 the electrical changes that occur during a single contraction. If the sciatic nerve, 

 A, of such a preparation be placed upon another muscle, B, as in fig. 405, then 



