540 THE OUTGO OF ENERGY 



Contractions will not be produced. If potas- 

 sium be applied to a contracting strip, the con- 

 tractions will cease. 



Combined Action of Sodium, Calcium, and 

 Potassium. Surround the ventricular muscle 

 with a solution containing sodium chloride (0.7 

 per cent), calcium chloride (0.0026 per cent), 

 and potassium chloride (0.035 per cent). This 

 is a modified " Einger " solution. 



Long-continued, rhythmic contractions will be 

 secured. 



Observers are not entirely agreed as to the 

 action of potassium and calcium on heart muscle. 

 The matter is of importance because there is 

 much probability that the rhythmic contractions 

 of the heart are the result of the constant chemi- 

 cal stimulus of inorganic salts present in the 

 blood. Most observers are agreed that the inter- 

 action of salts of sodium, calcium, and potassium 

 is essential. 



The fact that the contraction of the heart 

 begins normally in the sinus may be due to a 

 greater sensitiveness of that part to chemical 

 stimulation. 



