824 CONTRACTION-WAVE IN MUSCLE 



It will be seen that the dotted lirfe runs closely parallel with the 

 straight line which represents an ideal dependence of speed of con- 

 duction upon electrical conductivity. The dotted line connects the 

 values secured when the muscle is immersed in a solution -saturated 

 with oxygen; while the dash line connects those obtained when the 

 muscle is exposed to media containing oxygen at air tension. 



The fact that in the presence of a stream of oxygen the transmis- 

 sion of the contraction-wave is possible even in solutions of very 

 low conductivity is an indication that processes of oxidation are 

 directly concerned in stimulation and in the propagation of the 

 excitation state. If the primary change in stimulation is an altera- 

 tion of the protoplasmic surface film, it would appear that in a me- 

 dium of a given electrical conductivity a certain minimal concentra- 

 tion of oxygen is necessary for the completion of this surface reaction. 

 Lillie has pointed out that such a relation of oxygen to a chemical 

 reaction at the cell surface is suggestive of conditions similar to those 

 of an electrolysis at an electrode. In this case it is "possible to re- 

 duce the current-strength through a wider range, and still have a 

 high rate of decomposition at the electrode, if the concentration of 

 the reacting substance is high, than if it is low. "^* In the present 

 state of knowledge of the chemical conditions determining the for- 

 mation of an active or "stimulated" region in living tissue, it is diffi- 

 cult to define clearly the role of oxygen in the stimulation process. 

 In general it seems most probable that free oxygen is required in the 

 return of the stimulated region to the resting state and in the prop- 

 agation of the contraction-wave after the local stimulation has 

 been aroused. If the analogy between activation in living tissues 

 and in oxidisable metals bathed by electrolyte solutions, e.g. iron 

 in nitric acid, is at all close, then the destruction of the surface film 

 at any region during the rise of the activation-wave should depend 

 upon a local reduction rather than upon an oxidation; apparently 

 when the reduction has reached its maximum an oxidation process 

 occurs, reforming the film and the passive or resting state is regained. 

 In other words, the local excitation state is to be regarded as an effect 

 resulting from the expenditure of energy in the stimulated region — 



^* Personal communication. 



