710 STUDIES IN GENERAL PHYSIOLOGY 



rhythmically when immersed in the solution of salts with a 

 monovalent kation- -I obtained contractions in Na, Li, Rb, 

 and Cs salts but that the addition of a small quantity 

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

 these rhythmical contractions. 1 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 so- 

 lution, 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 solu- 

 tion 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 anni- 

 hilates this toxic action. The amount of calcium neces- 

 sary 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. 2 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 con- 

 centration equal to the concentration of the sodium chloride 

 in the sea- water (about f m), not a single egg can develop 

 into an embryo. If, however, a trace of a calcium salt is 



1 Part II, p. 518. 



2 Part II, p. 539; Archiv fur die gesammte Physiologic, Vol. LXXX (1900), p. 229 



