1913.] Oxygen Tension of Tissues during Activity. 217 



at the silver electrode. If, however, the usual electrical change is due to 

 an increased permeability of a membrane to negative ions both silver and 

 calomel electrodes will be equally affected, and hence the Ringer solution 

 may become positive from diffusion of hydrogen ions in my experiments, 

 whilst with the usual arrangement of electrodes the negative charge at 

 the membrane overbalances that due to the diffusion of the hydrogen ion. 

 The potential due to diffusion of the hydrogen ion should be reduced>to a 

 minimum by excess of indifferent electrolyte in the Ringer solution and 

 muscle lymph. 



Hydrogen Ions. 



Galeotti (loc. cit.) used a hydrogen electrode to measure the hydrogen ion, 

 but there is one objection to this electrode, namely, that if the electrode and 

 the tissue in contact with it are saturated with hydrogen the behaviour of the 

 tissue may be abnormal. To avoid this difficulty I have used a different form 

 of electrode. Galeotti added the action potential to his observed potential, 

 but until we know the true cause of the action current we cannot decide 

 whether or no this addition is legitimate. 



The oxygen electrode was not applicable and the reason for this will be 

 found in the third section of this paper. 



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

 wire covered with manganese dioxide.* The arrangement of the electrodes was 



Pt | Mn0 2 | muscle | Ringer solution | HgCl | Hg. 



Using this arrangement and compensating as before, on stimulating the 

 muscle the platinum electrode showed a very strong positive potential ; so 

 maxked was the effect that a deflection was obtained by a single break shock. 

 This cannot be due to negative ions diffusing into the Ringer solution, because 

 in the ratio (u—v)/(io + v) the hydroxyl ion is the only one that would give any 

 appreciable negative value and the liberation of hydroxyl ions would be more 

 effective in making the manganese dioxide electrode negative. Therefore, it 

 is evident that hydrogen ions are liberated during muscular contraction. 



Oxygen Tension. 



Many text-books contain the statement that there is no oxygen tension in 

 tissues. The author has pointed out that there must be some oxygen tensionf 

 and Verzar has shown, by an indirect method, the limiting values for sub- 

 maxillary gland and muscle.} 



* 0. F. Tower, ' Zeitschr. f. physik. Chem., ! 1900, vol. 32, p. 566. 

 t H. E. Roaf, ' Brit. Med. Journ.,' September 28, 1912. 

 X F. Verzar, ' Journ. Physiol.,' 1912, vol. 45, p. 39. 



