iv ELECTROMOTIVE ACTION IN MUSCLE 355 



the muscle. The size of the deflection was in many cases a little 

 smaller than when a sartorius provided with an artificial cross- 

 section is connected in circuit from cut surface to corresponding 

 point of the upper surface. Here diminished excitability goes 

 hand in hand with negativity of muscle-substance, and just as 

 this may be simply neutralised by washing out with physiological 

 NaCl solution, so too in regard to current. A few minutes 

 suffice to reduce the P.D. to a mere trace, which, with longer 

 washing, is also abolished, so that the muscle is once more 

 as at the beginning of the experiment free from current and of 

 normal excitability. The same result is obtained from the current- 

 less (parelectronomic) gastrocnemius by painting the expansion 

 of the tendo achilles with fluid, and the ascending current 

 obtained in cousecp:ience is well developed and of the same 

 order as the normal demarcation current (16). This very fact, 

 however, makes it the more remarkable that the " potassium cur- 

 rent " should be so easily neutralised by washing out with an 

 indifferent fluid, as is once more exhibited in a striking manner 

 on the gastrocnemius ; it suffices, after the muscle-substance at 

 the tendo achilles has become strongly negative from painting 

 with dilute solution of potass -salt, to wash it for a few 

 moments with 34 NaCl solution, in order as with the 

 galvanometer to replace the original, currentless condition. 

 This shows that the prejudicial effect of the solution can only 

 have extended to the extreme ends of the obliquely inserted 

 fibres. From these experiments the current-developing properties 

 of every artificial cross-section of a muscle are also easily inter- 

 preted, since acid potassium phosphate is always formed when 

 the muscle-substance becomes rigored. 



In opposition to the " potassium currents," those differences 

 of potential which appear on treating currentless muscle in the 

 same way with very dilute acid solutions (e.g. lactic acid) seem to 

 depend on much deeper chemical changes in the muscle-substance, 

 since no amount of washing will neutralise them, although they 

 are weaker than those produced by salts of potash. 



Du Bois-Reymond laid down the principle that no more 

 delicate test of the chemical sensibility of the muscle-substance 

 to any fluid can be devised than to moisten the natural cross- 

 section of a parelectronomic muscle with the solution, and to 

 observe the changes thus produced in the electrical condition of 



