302 THE EQUILIBRIUM OF COLLOID AND 



for its contractions, but the structural mechanism or machine for 

 oxidation has been interfered with and the cells can no longer 

 draw on their supply of stored energy. 



That this is the true state of the case is shown by the effects 

 of adding quite minimal traces of soluble salts of calcium and 

 potassium to the pure sodium chloride solution, when the spon- 

 taneous beating of the heart commences and goes on for hours, 

 and even days, in a regular and automatic manner. 



The amounts of potassium and calcium salts necessary to 

 bring out this profound difference in behaviour of the heart muscle 

 are strikingly small, the optimum amount of potassium chloride 

 required being only about 1 part in 10,000. More than an 

 exceedingly minute trace must not be added or the heart will 

 be stopped by the excess. There is only a certain range of con- 

 centration which must not be passed in either direction or the 

 heart will not beat normally. The meaning of this range will be 

 pointed out later. 



These important experimental results were first demonstrated 

 by Sidney Ringer in the case of cardiac muscle of the frog heart; 

 the complete generality of their application in all cells and tissues, 

 and the causes underlying them, are only in recent times becoming 

 generally appreciated, but the delicate and lightly balanced labile 

 equilibrium between the colloids of the cell protoplasm and the 

 osmotic pressures or concentrations of the inorganic ions and other 

 crystalloid constituents is perhaps the most important and funda- 

 mental fact in the whole of biology. 



The inorganic ions are sufficient in the case of the more slowly 

 oxidising cardiac muscle of the heart of the cold-blooded animal 

 to maintain for lengthened periods an automatic rhythmic beat; 

 the sufficient amount of oxygen for the oxidation being capable 

 of being carried at the partial pressure of one-fifth of an atmo- 

 sphere that the atmospheric oxygen possesses, and the combustible 

 organic material coming from the store in the cardiac muscle cells. 

 But in the case of the mammalian heart, the oxygen pressure 

 must be increased to nearly a whole atmosphere of pure oxygen 

 by bubbling oxygen gas through the Ringer's saline heated to 

 mammalian body temperature in a flask attached to the perfusion 

 cannula, before a normal heart-beat can be obtained. This in- 

 creased oxygen pressure supplies the place of the red blood- cor- 

 puscles which in the body are able to carry a sufficiency of oxygen 



