358 LECTURE XVI. 



standpoint so that definite conclusions may be drawn. It may be well to 

 cite one or two examples showing that, in fact, there is a specific action of 

 the inorganic salts. Overton * has shown that the muscles of a frog will 

 retain their normal volume in a 0.7 per cent solution of common salt, and 

 remain excitable at the end of 40 to 48 hours. In concentrated salt 

 solutions their volume is diminished, whereas in dilute solutions it increases. 

 Solutions of grape-sugar, cane-sugar, milk-sugar, mannitol, alanine, 

 asparagine, etc., having the same osmotic pressure as the 0.7 per cent 

 common salt solution, are equally indifferent as regards the osmosis. In 

 such solutions, however, the excitability of the muscle is soon lost. On 

 adding a little common salt to one of these solutions, however, it is again 

 possible to excite the muscle. In fact, 0.068 to 0.074 per cent of salt suffices 

 to render this effect. The next question is whether a change of the anion 

 (Cl) keeping the cation (Na) constant will have any effect. It was found 

 the chloride could be replaced successfully by equivalent amounts of the 

 bromide, nitrate, sulphate, bicarbonate, chlorate, acetate, and secondary 

 phosphate of sodium, showing that the anions had no influence here. In 

 a series of further experiments the cation was changed, and it was found 

 that the sodium could be replaced by lithium alone, while potassium, 

 calcium, magnesium, strontium, and barium salts were unable to preserve 

 the excitability of the muscle. It is perfectly obvious, therefore, that the 

 sodium ions, besides serving to maintain a definite osmotic pressure, also 

 exert a quite specific action upon the contractility of the muscle. 



Jacques Loeb 2 succeeded in performing a Very pretty experiment. If 

 the medusa Gonionemus be placed in a solution of cane-sugar or of glycerol, 

 the osmotic pressure of which corresponds to that of the ocean, its rhythmic 

 pulsation ceases immediately. This is not the case, however, if a solution 

 of sodium chloride or bromide is used in the above experiment. 



Loeb showed, moreover, that the presence of the sodium ions alone 

 was not sufficient to maintain the contractility of the muscle. In a 0.7 per 

 cent solution of common salt the muscles of a frog after about an hour 

 exhibit rhythmic contractions which last for over 24 hours. It appears 

 as if the sodium ions irritate in some way the muscular fibers. It has 

 even been stated that they have a poisonous effect. It is exceedingly 

 interesting that it is possible to combat this irritation of the sodium ions 

 (also obtained with rubidium and caesium ions) by the addition of the 

 bivalent calcium, strontium, magnesium and manganese ions. This 

 effect is not, however, due merely to the valence of the ion, for the bivalent 

 barium, zinc, cadmium, and lead ions do not act in the same way. On 

 the other hand the monovalent potassium ion has an effect opposite to 

 that of the monovalent sodium ion. It is particularly interesting that 



1 Pfluger's Arch. 92, 115 and 346 (1902). 



2 Am. J. Physiol. 3, 383 (1900). 



