THE RELATION OF THE HEART-BEAT TO ELECTROLYTES. 175 



The " Einger's solution " most commonly employed in the physio- 

 logical laboratory contains chiefly sodium chloride with small quantities 

 of potassium and calcium chlorides and of sodium hydrogen carbonate. 

 The actual concentrations of the salts employed differ according to 

 the animal used ; for the frog the total concentrations should be about 

 •125 Mol. If the concentration of sodium chloride be called 100 the 

 relative concentrations of the other salts may be taken as 2*5 of 

 potassium chloride, 2 of calcium chloride, and 1*5 of sodium hydrogen 

 carbonate. This solution, simplified by the omission of the last-named 

 ingredient, still maintains the heart-beat in a satisfactory manner. We 

 shall return in a moment to the function of the sodium bicarbonate. 

 Its presence is nonessential. Eemoval of the potassium salt leads to 

 an alteration in the character of the beats, the systolic phase becoming 

 prolonged, but does not necessarily cause arrest or even weakening of 

 the beats. With a solution consisting only of distilled water with 

 sodium and calcium chlorides and some dissolved oxygen, if the concen- 

 tration of the Ca is carefully adjusted, the frog's heart may be kept 

 beating vigorously for prolonged periods. 



Eemoval of the calcium from the perfusion fluid is immediately 

 followed by great weakening of the contractions, which in the course 

 of a few minutes become exceedingly feeble and before long cease 

 altogether, the heart remaining in a relaxed state. When the calcium 

 is replaced the beats start again at once and become as vigorous as at 

 the start. In the frog, as Einger showed, the calcium may effectively 

 be replaced by strontium. It may also be replaced by barium, but 

 only to a very limited extent, for in a short time barium causes arrest 

 of the heart in a firmly contracted state. 



It should be noted that practically any soluble salt of calcium may 

 be used in place of the chloride. The ionic theory is peculiarly accept- 

 able to the physiologist in that it gives concrete expression to the fact 

 so often encountered, as here, that all solutions of a particular metal, 

 where on physico-chemical theory it should be in the same ionic con- 

 dition, present in common certain definite physiological actions. We 

 may say that the calcium ion is essential for the activity of the heart. 

 There is reason to think that the calcium forms with some constituent 

 of the heart muscle a readily dissociated compound, whose presence is 

 a cardinal factor in the activity of heart muscle. The closely similar 

 strontium ion can form a compound so similar to the calcium compound 

 that it can fill the same niche in the architecture of the muscle, while 

 the barium ion may best be pictured as forming a compound of similar 

 composition but probably almost irreversible, perhaps through great in- 

 solubility. No metal otlier than these has been found to replace calcium. 



