PROPERTIES OF THE HEART MUSCLE. 501 



mainly to the organic substances in the blood, it has been shown in 

 recent years that the inorganic salts are the elements whose influence 

 upon the heart beat is most striking. These salts are in solution 

 in the liquid of the tissue, and are therefore probably more or less 

 completely ionized. Attention has been directed mainly to the 

 influence of the metallic ions, the cations, of which three are es- 

 pecially important, namely, the sodium, the calcium, and the 

 potassium. 



The Action of the Calcium, Potassium, and Sodium Ions in 

 the Blood and Lymph. It has long been known that the heart 

 of a frog or terrapin may be kept beating normally for hours after 

 removal from the body, provided it is supplied with an artificial 

 circulation of blood or lymph, so arranged that this liquid enters 

 the heart through the veins from a reservoir of some sort and is 

 pumped out through the arteries leading from the ventricle. It 

 was first shown by Merunowicz, working under Ludwig's direction, 

 that an aqueous extract of the ash of the blood possesses a similar 

 action. 



Ringer afterwards proved that the frog's heart can be kept 

 beating for long periods upon a mixture of sodium chlorid, potassium 

 chlorid, and calcium phosphate or chlorid, and he laid especial 

 stress upon the importance of the calcium. This work was after- 

 wards confirmed and extended by Howell, Loeb, and others, who 

 attempted to analyze the part played by the several ions.* If 

 a frog's or terrapin's heart is fed with a solution of physiological 

 saline (Nad, 0.7 per cent.) it beats well for a while, but the 

 beats soon weaken and gradually fade out. If in this condition 

 the heart is fed with a proper mixture of sodium, potassium, 

 and calcium chlorids it beats vigorously and well for very many 

 hours. A solution containing these three salts in proper propor- 

 tions is known usually as Ringer's mixture. The exact com- 

 position has been varied by different workers, but for the heart 

 of the frog or terrapin the following composition is most effective : 



NaCl. . = 0.7 per cent. 



KC1.. = 0.03 " " 



CaCl = 0.025 " 



The addition of a trace of alkali, HNaCO 3 , 0.003 per cent., 

 often increases the effectiveness of the solution, but it can not be 

 considered an essential constituent in the same sense as sodium, 

 potassium, and calcium. It has been shown, moreover, that even 

 the mammalian heart can be kept beating for long periods when 

 fed with a Ringer solution if provision is made for a larger supply 



* For literature and discussion see Howell, " American Journal of Phys- 

 iology," 2, 47, 1898, and 6. 181, 1901. 



