PROPERTIES OF THE HEAPT MUSCLE. 565 



NaCl = 0.7 per cent. 



KCl = 0.03 " " 



CaCl = 0.025 " " 



The addition of a trace of alkali, HNaCO,?, 0.003 per cent, in- 

 creases the effectiveness of the solution probably by giving to 

 it a slightly alkaline reaction approximating that of normal blood. 

 It has been shown, moreover, that even the mammalian heart 

 can be kept beating for long periods when fed with a Ringer solu- 

 tion 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 forms 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.; CaCl2, 

 0.024 per cent.; KCl, 0.042 per cent.; NaHCO,,, 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 maintained heart 

 activity. It seems probable from the work of Meltzer that mag- 

 nesium enters also into the balanced activity normally exerted 

 upon the heart and other tissues by the inorganic salts. It has an 

 inhibitory or moderating influence upon the action of the other 

 cations. As a possible explanation of this interesting relation it 

 has been pointed out that the ancestral forms of animal life were 

 probably pelagic, and that the composition of the internal me- 

 dium, the body fluid or blood, was determined by that of the ex- 

 ternal medium, the sea-water, f Regarding the specific part taken 



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

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



t A. B. Macallum, "Transactions College of Physicians," Philadelphia, 

 1917. 



