PROPERTIES OF THE HEART MUSCLE. 521 



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.; 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, is said to increase its efficiency. 

 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 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 

 started again promptly by adding calcium chlorid in right amounts 

 to the oxalated blood. Regarding the specific part taken by each 

 of the cations in the production of the alternate contractions and 

 relaxations, much diversity of opinion exists, owing to our ignorance 

 of the chemical changes going on in the heart during systole and 

 diastole and to the difficulty of controlling experimental conditions. 

 Thus, while it is an easy matter to control accurately the com- 

 position of the liquids supplied to the heart, a variable and uncon- 

 trollable factor is introduced by the fact that within the tissue 

 elements themselves there is a store of combined calcium, potassium, 

 and sodium which may serve to supply these elements to a greater 

 or less extent to the tissue liquids. 



The controversial details upon this question can not be presented 

 in an elementary book, but the following brief statements may 

 be made regarding one view of the specific effects of the separate 

 cations: (1) The sodium salts in the blood and lymph take the 

 chief part in the maintenance of normal osmotic pressure. The 



