356 ELECTRO-PHYSIOLOGY CHAP. 



the section. From this point of view, the potassium salts in 

 general must be regarded as distinct muscle poisons, while the 

 corresponding sodium combinations at the same molecular weight 

 are almost innocuous, and even possess in many cases a distinct 

 power of regenerating excitability (]N"a 9 CO g ). In consideration of 

 this last fact a fluid cannot therefore be termed indifferent for 

 the muscle, where no perceptible current is developed from 

 its local application. Even the physiological NaCl solution 

 (0'5-0'7 %) which, if applied for hours to the natural cross- 

 section of an uninjured, currentless muscle, causes no trace 

 of a demarcation current, produces, according to F. S. Locke 

 (17), a visible increase of excitability, as has long been known 

 with regard to stronger solutions. Certainly, however, the 

 current-developing properties of a solution must be taken as the 

 measure of its injuriousness to the muscle, and though Nasse 

 takes a 0'7 % solution of KC1 or KN0 3 as equal to a 

 0'2 1*5 % solution of NaCl, his conclusion is not borne 

 out by galvanometer experiments. If the lower end of a 

 curarised sartorius dips into even a 2 % solution of NaCl, 

 no perceptible demarcation current will have appeared after 10 

 to 20 minutes, or there may even be a faint deflection in the 

 opposite direction, in the sense of a descending current in the 

 muscle. Engelmann, too, found in his investigations into the 

 electromotive properties of the uninjured surface of the frog's 

 heart, that solutions of NaCl, if stronger than 0'6 / Q , made 

 the points in contact with them positive in regard to other points 

 of the surface of the heart. Still less deleterious than NaCl is the 

 action of other neutral sodium salts upon the substance of the 

 muscle, e.g. Na 2 S0 4 and NaN0 3 , which, even in strong solutions 

 (4-12 / Q \ develop only a small amount of current, as 

 compared with the local effects of equivalent solutions of NaCl or 

 the corresponding salts of K upon the sartorius. Even alkaline 

 sodium carbonate, which augments the excitability of striated 

 muscle in a remarkable degree, either produces no current in 

 dilute solutions, or a weak inverted current only, in the sense of 

 positivity of the immersed end of the muscle (18). 



The opinion generally prevails that distilled water is rapidly 

 and energetically inimical to muscle-substance, e.g. Kiihne con- 

 cludes from the fact that a frog's sartorius dipping into distilled 

 water loses its excitability more quickly than a muscle dipping 



