in ELECTRICAL EXCITATION OF MUSCLE 223 



normal, and highly excitable, with the sole exception of the 

 ends of the fibres on one side, at the point at which 

 excitability of the contractile substance has been artificially 

 lowered by any reagent ; we should then be theoretically justified 

 in the expectation that on sending current longitudinally through 

 such a muscle, the effects of the closing, as of the opening; 

 stimulus, would in a marked degree be found to depend upon the 

 direction of the current^ since the same stimulus would, in the 

 one case, act upon normally excitable, in the other upon 

 " fatigued," substance. In proportion as the local depression 

 of excitability is higher at one end of the muscle, the more 

 plainly would the difference in the excitatory action of the two 

 directions of current come into evidence. And further, the 

 extension of " local fatigue " cannot fail to affect the conse- 

 quences of excitation, as appears from the following considera- 

 tion. If we picture the muscle as divided into zones of equal 

 magnitude, and assume that excitability is depressed in the end- 

 zone only, while it remains normal in the others, it must 

 obviously be possible to find a stimulus of the right strength 

 to discharge an excitatory process in the former, which will 

 propagate itself by conduction, and thus bring about a perceptible 

 change of form, either in the entire muscle, or at least in the 

 proximal half of it. But the same minimal stimulus will fail 

 to produce this effect if the excitability of the zones immediately 

 adjacent to the terminal section is depressed in the same pro- 

 portion. For in such a case the excitation, starting with the 

 same strength as before, dies out within a very short area, or 

 gives rise to a weak persistent contraction only. 



Such a muscle as we have been imagining can, in fact, be 

 produced artificially. With careful exposure it results from 

 treatment of one or other end of the sartorius with weak solu- 

 tions of certain salts (e.g. acid potassium phosphate, and meat- 

 juice, the effect of which is probably due to these salts), which do 

 not essentially alter the structure of the immersed section of the 

 muscle, but partially depress its excitability, giving the oppor- 

 tunity of determining the correspondence between experimental 

 data and theoretical conclusions. 



But the electrical current itself, by repeated closure with 

 unaltered direction of current, induces still more completely 

 a condition of the muscle, in which it reacts only in one, 



