ELECTROLYTES AND THEIR ACTION 209 



3 c.c. of the calcium chloride solution were added, and a further 3 c.c. before each step in the 

 tracing. We note the increase of tonic contraction brought about by each addition. At k 

 potassium chloride was added, but, although it diminished the systolic condition, the size 

 of the beat was rather decreased ; in fact, the antagonism is not complete when there is 

 excess of either calcium or potassium much beyond the normal proportion. Finally at I 

 normal Ringer solution was perfused. 



It is a remarkable fact that the proportion of sodium, potassium, and calcium 

 ions in sea water is almost identical with that found by Ringer to be the best 

 for maintaining the beat of the heart, although the total concentration in 

 sea water is higher. Magnesium salts, however, are present in sea water, 

 in addition to those mentioned. The presence of magnesium does not appear 

 to be necessary in an artificial physiological saline solution, although Neu lurch 



FIG. 63. ACTION OF ELECTROLYTES ON THE HEART OF THE TORTOISE. 



a, Excised heart before perfusion. 



b, Perfusion with sodium chloride, 075 per cent., sodium bicarbonate, O'Ol per cent. 



c, Addition of 3 c.c. of O'l molar calcium chloride to 100 c.c. 



d, Potassium chloride added, 6 c.c. of O'l molar to 100 c.c. of the mixture containing sodium and calcium salts. 



e, Pure sodium chloride again. 



/, Potassium chloride, 6 c.c. to 100. 



g, Calcium chloride added. 



h, 3 c.c. calcium chloride added before each step in the tracing. 



k, More potassium chloride added, in amount'corresponding to the calcium chloride present. The tonic action of 



the calcium is partly abolished, but the beat does not return to its normal height. 

 /. Normal Ringer's solution. 



6-cand e-/=Na alone, c-rf=Na+Ca, d-e and <7-A = Na+Ca+K,/-#=Na+K. 



(1912) found that the contractions of the excised intestine of the rabbit were 

 more regular when magnesium was present. 



If we look at the i-elative proportions of these ions in blood serum and in 

 sea water, viz. : 



(Macallum, 1910, p. 603) 



we notice that the proportion of calcium to sodium is very similar and that 

 of potassium to sodium is not very far different in the two solutions, but 

 there is a great excess of magnesium in sea water. The probable reasons for 

 the divergences will be seen presently. Bunge (1894, p. 120) made the suggestion 

 that the high content in sodium chloride of the blood of land vertebrates in 

 comparison with that of their surroundings is an inheritance from marine 



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