ELECTROLYTES IN LIVING MATTER 87 



The contact irritability depends (as Loeb suggested) on the disturbance 

 of the normal ratio of salts in the muscle. Perhaps it is the disturbed 

 ratio between the potassium and calcium salts which makes the contact 

 reaction possible." Of course the experiment of Zoethout does not 

 explain why the contact reaction only occurs when the muscle is taken 

 out of the citrate solution. 



I am inclined to believe that not only the K but also the Na-salts 

 are concerned in this reaction ; but it is certain that Zoethout's observa- 

 tions establish the fact that the antagonism between K and Ca-salts 

 is to be considered in the theory of animal irritability and stimulation. 

 The statement contained in my older publications, namely, that 

 possibly the substitution of Na for Ca, or vice versa, caused the twitch- 

 ing of the muscle must be modified so as to include also the substitution 

 of K for Ca, or vice versa. Perhaps it may be said that the substitution 

 of any univalent cation for Ca in the muscle, or vice versa, causes a 

 twitching. As of the univalent metals, however, only Na and K occur 

 in the tissues, they are the principal ones to be considered. It seems 

 from these observations and others, all of which cannot be considered 

 in this short sketch, as if indeed the substitution of Na or K for Ca-salts, 

 or vice versa, is the essential feature of the twitching or of muscular 

 stimulation. It would be of the utmost importance to determine which 

 of the two possible changes was the real cause. We know that in general 

 a substitution of Ca for K or Na in colloids favors the formation of 

 more solid or insoluble compounds, e.g. in the case of soaps. In the 

 case of the coagulation of blood or milk, it is also obvious that Ca in 

 moderate quantities favors coagulation. 



Ringer had already observed that barium salts have a stimulating 

 effect upon muscle, and I have been able to confirm this observation. 

 A pure solution of any soluble barium salts gives rise to powerful rhyth- 

 mical contractions of the muscle ; and the threshold for this stimulation 

 is much lower for Ba than for the corresponding Na-salts. In a NaCl 

 solution the contractions last longer than in a BaCl 2 solution, on account 

 of the greater toxicity of the BaCl 2 . I expected from this that a pure 

 solution of CaCl 2 or SrCL, might act similarly to BaCl 2 , but this does 

 not seem to be the case for the muscle. Two years ago, however, I 

 found some new facts concerning the influence of salts upon rhythmical 

 contractions of the center of a Californian jellyfish, Polyorchis, which 

 meet this expectation.* If the margin containing the central nervous 

 system of this Medusa be cut off from the center of the swimming bell, 

 the center no longer contracts spontaneously in sea water; nor if it 

 be put into a pure NaCl solution of about the concentration of the 



* Not yet published. 



