MUSCLE CURRENTS 



of the amount of vitality possessed by muscle. A weak muscle 

 can do less work than a strong muscle, and a given muscle in 

 the course of fatigue, or of that last act of life that we call 

 death, can give less and less extensive contraction, and effect 

 a smaller and smaller amount of work. Pari passu with declin- 

 ing contraction we witness declining electromotive response, and 

 we admit or assume that the common substratum of the decline, 

 whether mechanical or electrical, is decline of chemical activity. 

 An excised muscle has been set up to show this parallelism 

 between mechanical and electrical response. A lever attached 

 to the tendon indicates to you, by its excursion on a smoked 

 glass plate, the extent or height of the mechanical movements 

 (contraction). A galvanometer connected to the muscle by 



Mechd.nicd.L Response. 



ELectric&L Response, 



FIG. 2. Simultaneous records of a series of muscular contractions, and of the 

 corresponding series of negative variations. The method and apparatus for obtaining 

 such records is described in the Appendix, p. 160, Fig. 63. 



wires and unpolarisable electrodes, indicates to you, by the 

 excursion of the reflected spot of light, the extent or voltage of 

 the accompanying electrical movements. The muscle is excited 

 indirectly, by excitation of its nerve, and, as you see, the two 

 sets of movements, mechanical and electrical, run an approxi- 

 mately parallel course both are large together or small to- 

 gether, and if one is absent, so is the other. You would notice, 

 however, on closer comparison, that the parallelism is not perfect, 

 the mechanical and electrical responses are not an exact replica 

 of each other, and the defect of correspondence is particularly 

 apparent in simultaneous records of the two sets of responses. 



I cannot at present enter further upon this difference, I think 

 it requires further study ; if you ask which of the two records is 

 the more faithful indicator of the chemical changes of which 



