220 ELECTRO-PHYSIOLOGY CHAP. 



that is required to produce these conspicuous manifestations 

 of electrical excitation. Most of the salts of potassium are 

 known to be acute muscle poisons, since when introduced in 

 bulk into the circulation, or applied locally, they exercise a 

 highly depressant, or inhibitory, action upon the excitability of 

 striated skeletal and cardiac muscle ; many acids are hardly less 

 inimical to muscle-substance, even when highly diluted. It is 

 easy to demonstrate that local treatment of one or the other end 

 of the sartorius with these substances, which are inimical to 

 excitability at the point of application, produces a reaction of 

 the muscle to current analogous to that with localised death of 

 the fibres. The method of experiment is the same as above. 

 The chemical substances to be investigated are diluted in various 

 degrees by moistening the thin (knee) end of the sartorius with 

 a pad of cotton-wool soaked in the fluid required, or by dipping 

 the vertically dependent muscle into it. The effects are most 

 striking with the application of highly dilute (1-2 %) 

 solutions of acid potassium phosphate, or a solution of meat- 

 juice saturated with the same. After five to ten minutes' per- 

 sistent action on the tibial end of the muscle, the excitability 

 to closure of the descending, and opening of the ascending, 

 current is invariably more or less diminished, so that the mani- 

 festations of contraction fail altogether, or are conspicuously 

 lessened, if the effective electrode is situated at the end of the 

 muscle that is undergoing chemical alteration (26). It must be 

 remarked that here, as in the previous experiments, it is not 

 complete abolition, but only diminution, of excitability to one 

 direction of the current, caused by local " fatigue," that ensues, 

 so that strong descending currents will still excite a sartorius 

 treated as above, although no perceptible movement of the muscle 

 responds to the impact of a weaker descending current, even 

 when its intensity is quite adequate to produce a maximal 

 closure excitation in an ascending direction. 



From these results we must conclude that in all the above 

 cases it depends not so much upon the actual death of the contractile 

 substance in any localised spot, as upon the consequences of chemical 

 alteration in the same, ivhether, and to what degree, the closing and 

 opening excitation become effective at the point of stimulation ; and 

 this is forced upon us still more by the fact that with local 

 application of dilute solutions of salts of potassium, the normal 



