PROPERTIES OF THE HEART MUSCLE. 571 



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 f = 0.025 " 



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

 often increases the effectiveness of the solution, but it cannot 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 

 of oxygen than can be obtained by simple exposure to the air. 

 For the irrigation of the isolated mammalian heart different 

 torms of Ringer's solution have been employed, but the mixture 

 most frequently used is that recommended by Locke, consisting 

 of NaCl, 0.9 per cent.; CaCl 2 , 0.024 per cent.; KC1, 0.042 per 

 cent.; NaHCO 3 , 0.01 to 0.03 per cent.; and dextrose, 0.1 per cent. 

 The solution is fed to the heart under an atmosphere of oxygen, 

 and with this solution Locke and others have kept the mammalian 

 heart beating for many hours. The dextrose, while not essential 

 to the action of the irrigating liquid, increases its efficiency, and 

 Locke* has shown that the sugar is apparently utilized by the 

 heart, since a considerable amount disappears from the solution 

 when the heart is beating strongly. The general fact that comes 

 out of these experiments is that the heart can beat for very long 

 periods upon what has been called an inorganic diet. Moreover, 

 the salts that are used cannot be chosen at random; it is necessary 

 to have salts of the three metals named, and substitution is possible 

 only to a very limited extent. Thus, strontium salts may replace 

 those of calcium more or less perfectly. 



It is evident that these salts play some very important part 

 in the production of the rhythmical beat of the heart; and analysis 

 has shown that the sodium, calcium, and potassium has each 

 its special role. We may say that the presence of these salts 

 in normal proportions is an absolute necessity for heart activity. 

 A striking experiment which shows the importance of the calcium 

 is to irrigate a terrapin's heart with blood-serum from which the 

 calcium has been removed by precipitation with sodium oxalate. 

 In spite of the fact that all other constituents of the blood are 

 present the heart ceases to beat, and normal contractions can be 



* Locke and Rosenheim, ''Journal of Physiology," 36, 205, 1907. See also 

 Knowlton and Starling, ibid. 45, 146, 1912. 



