218 Liberation of Ions and Oxygen Tension of Tissues. 



The electrode used to replace one of the calomel electrodes was a piece of 

 platinum wire covered with platinum black. The arrangement was 



Pt | muscle | Kinger solution | HgCl j Hg. 



The platinum electrode in oxygen or air gave results which when the 

 muscle contracted showed sometimes a positive potential, sometimes after a 

 slight positive potential a negative potential, and sometimes only a negative 

 potential. The formula for the potential at a gas electrode contains the ratio 

 ^/T/p, where P = the partial pressure of the gas and p = the osmotic pressure 

 of the corresponding ion. From this ratio it can be seen that a fall in 

 oxygen tension would produce the same effect as a rise in hydroxyl* (fall in 

 hydrogen) ion concentration. Therefore, there are two factors to consider, 

 an increase in hydrogen ions, which tends to make the platinum positive, and 

 a fall in oxygen tension, which tends to make it negative. The deflections of 

 the galvanometer would, therefore, be explained as a rise in hydrogen ion 

 concentration which is frequently overbalanced by a fall in oxygen tension. 



The proof of this is very easy. When the access of air is prevented by a 

 piece of rubber sheeting placed over the platinum wire as it lies against the 

 muscle, the galvanometer may not show any deflection, but on stimulating the 

 muscle the platinum becomes negative, thus indicating a fall in oxygen tension. 

 This experiment has been frequently repeated and it is possible to convert 

 one form of reaction into another. When the electrode is exposed to air 

 the fall in oxygen tension is less, and hence, especially at the beginning of 

 stimulation, the increase of hydrogen ions causes the platinum to become 

 positive, but when the electrode is covered the fall in oxygen tension is 

 greater, so that the rise of hydrogen ions is masked and the platinum always 

 becomes negative. It is evident that this result may form the basis of a 

 method for the direct measurement of oxygen tensions in tissues. 



The results so far obtained are purely preliminary. Measurements of the 

 time relations and the actual potential produced will show whether the 

 liberation precedes, accompanies or succeeds the muscular contraction and will 

 give some approximation to the relative increase in ionic concentrations. 



Finally, it must be pointed out that the concentrations of ions measured are 

 those in the lymph on the surface of the muscle. An increase may be due to 

 an actual increase in ionic concentration inside the muscle or to an increase 

 in permeability of a membrane previously impermeable to the ion measured. 



* Since the concentration of the doubly charged oxygen ion is proportional to the 

 square of the hydroxyl ion concentration. 



