MEMBRANE CHANGES DURING STIMULATION 345 



surface-film to its previous continuous and semi- 

 permeable state; yet the film may require some further 

 structural or chemical modification before it is in a 

 condition favorable for stimulation and transmission. 

 The relative refractory period seems to correspond to 

 the time during which those regulatory or restorative 

 changes are proceeding in the newly re-formed film. 



These general considerations receive support of an 

 indirect kind from my recent experiments on transmission 

 and recovery of transmissivity in passive iron wires 

 immersed in nitric acid solution.^ In this inorganic 

 model there is also a refractory or non-transmissive 

 period immediately following the passage of an activation- 

 wave. During the progress of the chemical reaction 

 following the activation of a passive wire in 60 per cent 

 HNO3, the metal exhibits the chemical and electrical 

 properties of ordinary or active iron, and is insusceptible 

 to further activation. This initial period . of activity 

 may be compared with the absolute refractory period 

 in the Hving tissue. Its onset is accompanied by a 

 variation of potential, the active metal becoming negative 

 (anodal) relatively to its previous condition by ca. 0.7 

 volt. After a brief interval of vigorous chemical reaction, 

 lasting from one to two seconds, the metal reverts 

 spontaneously to the passive state, the effervescence 

 ceases, and the potential immediately becomes again 

 positive. During the first minute or so after this 

 automatic repassivation it is found impossible to reactiv- 

 ate the metal completely by local mechanical or chemical 

 treatment; e.g., touching the wire with zinc produces a 

 brief and partial activation which is transmitted fo;* 



^ Jour. Gen. Physiol., Ill (1920), 107, 129, 



