ELECTRICALLY CHARGED MOLECULES. 77 



1 succeeded in doing this three years ago. It was known that a frog's 

 muscle gives rise to twitchings or rhythmical contractions when 

 immersed in certain solutions. I showed that such contractions, 

 occurred only in solutions of electrolytes, and not in solutions of non- 

 conductors (distilled water, various sugars, glycerine, urea). Soon 

 after I showed the same to be true also for the rhythmical contractions 

 of the medusae. From observations made in my laboratory, the same 

 fact was shown to hold for the turtle's heart by Mr. Lingle, and for 

 the lymph hearts of the frog by Miss Moore. I am confident that 

 this fact will be proved universally. 



In the physiology of the heart one frequently encounters the state- 

 ment that calcium is the stimulus for the contraction of the heart. 

 I had found that a muscle is able to twitch rhythmically when immersed 

 in the solution of salts with a monovalent kation, — I obtained contrac- 

 tions in Na-, Li-, Kb-, and Cs-salts, — but that the addition of a small 

 quantity of a bivalent kation — Ca, Mg, Sr, Ba, Be, Mn, Co — inhibits 

 these rhythmical contractions. This seemed to be a direct contradiction 

 to the statement that calcium salts are the 'cause' of the heart-beat. 

 The significance of the calcium had to be looked for, then, in another 

 direction. It was soon found that the muscle, the apex of the heart, 

 and a medusa contract rhythmically in a pure sodium chloride solution, 

 but that they soon come to a standstill. If, however, a trace of a soluble 

 calcium salt is added to the sodium chloride solution, the contractions 

 continue much longer. I concluded from this that the pure sodium 

 chloride solution acts, in the long run, as a poison — that is to say, 

 brings about definite but at present unknown physical changes in the 

 protoplasm — but that a trace of a calcium salt annihilates this toxic 

 action. The amount of calcium necessary for this antitoxic effect is of 

 course much smaller than the amount necessary to inhibit the rhyth- 

 mical contractions. Soon after I succeeded in demonstrating con- 

 clusively the poisonous effect of a pure sodium chloride solution, and 

 the annihilation of this effect by calcium. The eggs of a marine fish 

 (Fundulus) develop normally in sea-water, but they can develop just 

 as well, as I had previously found, in distilled water. The addition of 

 ions from the outside is consequently not necessary to the development 

 of this animal. I found, now, that, if the freshly fertilized eggs of 

 this fish are put into a pure sodium chloride solution having a concen- 

 tration equal to the concentration of the sodium chloride in the sea- 

 water (about % m), not a single egg can develop into an embryo. If, 

 however, a trace of a calcium salt is added to the sodium chloride solu- 

 tion, as many eggs develop and in just as normal a manner as in 

 ordinary sea-water. The calcium ions in this case undoubtedly serve 

 the purpose of annihilating the poisonous effects of a pure sodium 

 chloride solution. 



