CRYSTALLOID IN LIVING CELLS 3 



has been di-tiTmined by that moment at which the concentration 

 in the protoplasm has reached a certain minimal value. 



The most important of the ions which have been washed out 

 of the cardiac muscle cells by the current of pure sodium chloride 

 solution are the potassium and calcium ions. It still possesses 

 abundance of combustible organic material to furnish the energy 

 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 

 fundamental 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 bsing carried at the partial pressure of one-fifth of an atmos- 

 phere 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 



