pH Changes of Muscle During and After Contraction

Since Meyerhof and Lipmann, 1 and Meyerhof, Moehle and Schulz 2 studied the exchange of CO₂ in frogs'muscle during fatigue, we know that under anaerobic conditions the pH of the muscle, when subjected to periodic stimulations, will first increase and then gradually decrease. However, the method applied by these authors does not show the pH changes during the activity itself, i. e., contraction and relaxation of the muscle. Margaria and Pulcher 3 attempted to show the pH change during contraction itself by coloring the muscle with bromocresol purple. They found a change in color during the contraction corresponding to an increase in pH of about 0.5. According to Margaria, 4 however, the same changes occur when the muscle is mechanically stretched. Later Margaria and von Muralt 5 described a photo-electric method with which it would be possible to record those changes of color. On summarizing, as far as I know, no records showing the pH changes during and after contraction have been published. I succeeded in obtaining such records during tetanus by an entirely different method. Its principle is to cover a part of the surface of the muscle with a glass electrode and to record the pH changes occurring on stimulation.

The glass electrode consists of a membrane of suitable glass sealed to the end of a tube of ordinary glass. This is the first of the two types of glass electrode described by MacInnes. 6 The glass membrane is brought into contact with the wet external surface of the muscle. Glass electrode, muscle, and a potentiometer are mounted in series in the grid circuit of a Pliotron tube F.P. 54 7 .