176 GEORGE RALPH MINES. 



It is of interest to find that these relations of the heart muscle to 

 Ca, Sr, and Ba are essentially the same, not only in other vertebrates 

 which have been studied, but also in the heart of the mollusc Pecten. 



So far then the features of immediate im])ortanee in the 2^^^ fusion 

 fluid for the heart appear to he the presence of certain concentrations of 

 sodium and of calcium ions, the p)rescnce of dissolved oxygen and the main- 

 tenance of the tempierature ivithin certain limits. 



• Keeping these conditions constant, let us consider the effects of 

 varying the composition of the fluid in certain other respects. 



Since we deal always in physiological work with aqueous solutions, 

 and since water is to a slight extent electrolytically dissociated, our 

 solutions always contain hydrogen ions and hydroxyl ions. In pure 

 water these are of course present in equal numbers, the concentration 

 of each, expressed in gram-ions per litre, being at room temperature 

 about 10-7. 



It follows directly from the general principle expressed in the law of 

 mass action that the addition to the water of any substance tending to 

 increase the concentration of hydrogen ions will reduce the concentra- 

 tions of hydroxyl ions. A similar shift in the equilibrium will be pro- 

 duced by the addition of any substance tending to remove hydroxyl 

 ions. The ratio of the H" to OH' is increased. An inverse change 

 is produced by the addition of OH' or the removal of H'. 



Knowing the dissociation constant of water, if the hydrogen ion con- 

 centration of any aqueous solution is given it is a matter of sunple 

 arithmetic to calculate the hydroxyl ion concentration and the ratio 

 between the hydrogen and hydroxyl ion concentrations for that 

 solution. 



To define the position of this H-, OH' equilibrium for any solution 

 it is sufficient therefore to state the hydrogen ion concentration of the 

 solution. This is expressed most conveniently as a logarithm. 



To avoid the constant repetition of the phrase " hydrogen ion con- 

 centration" we may adopt Sorensen's notation in which the symbol 

 P + is followed by the logarithm of the hydrogen ion concentration, 



H 

 the minus sign being understood. Thus describing a solution as being 

 of P + 7'07 means " the hydrogen ion concentration of the solution is 



H 

 equal to lO-'^"^'' gram ions per litre." 



An aqueous solution whose P+ at 18° 0. is 7"07 is neutral in reaction. 



H 

 If the P+ is numerically less than 707 the solution is acid, if greater 

 H 



