I 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 medusæ. 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 statement 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 contractions 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 rhythmical contractions. Soon after I succeeded in demonstrating conclusively 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 concentration equal to the concentration of the sodium chloride in the sea-water (about 5/8 m), not a single egg can develop into an embryo. If, however, a trace of a calcium salt is added to the sodium chloride solution, 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.