406 



The Acidity of Muscle during Maintained Contraction. 



By H. E. Eoaf. 



(Communicated by Sir Charles S. Sherrington, Pres. E.S. Eeceived March 11, 1922.) 

 (From the Departmeot of Physiology, London Hospital, Medical College.) 



In 1913, I described a method for recording changes in hydrogen-ion 

 concentrations in tissues, by means of a manganese dioxide electrode in 

 combination with a calomel electrode (1). By this method it was shown that 

 the acidity of muscle probably increased at the same time as, or slightly 

 before, the tension increased, and that the acidity decreased as the muscle 

 relaxed (2). 



In a paper, which appeared as this note was being prepared for publication, 

 Bitchie* states that he has been unable to detect a variation in acidity by the 

 use of manganese dioxide electrodes. I am inclined to think that his failure 

 is due to the injury to the muscles on insertion of wires into its substance. 

 In my own experiments the wires rest on the surface of the muscle. 



The electrical change observed by me is not due to spread of potential from 

 the stimulating circuit, because in some records a potential is recorded 

 corresponding to the time of stimulation. This potential is quite separate 

 from the larger potential ascribed to the acid production, and it may be in the 

 same or in an opposite direction from that which accompanies the contraction. 



In my experiments L took precautions to minimise movement of the 

 electrode on the surface of the muscle, and any slight movements are probably 

 less important with the sartorius than with the gastrocnemius. Change of 

 potential, due to movement of the electrode, would probably vary in direction, 

 whilst with the manganese dioxide electrode the change is always in the same 

 direction. If the electrode did move on the surface of the muscle it is unlikely 

 that the potential would return to its former value, as it is seen to do in most 

 of my records. 



Other forms of metallic electrodes would give changes of potential depending 

 on the chemical reactions that take place in contact with them. 



I do not think that the change shown by a manganese dioxide electrode is 

 due to polarisation. If the electrodes are so placed that no difference of 

 potential is shown during contraction by non-polarisable electrodes, it is 

 difficult to see how any difference of potential will be produced when one 

 calomel electrode is substituted by a manganese dioxide electrode and the 



* A. D. Eitchie, ' Journ. Physiol.,' vol. 56, p. 53 (1922). 



