RALPH S. LILLIE 115 



activating one of the wires the needle of the instrument shows at once 

 a rapid initial excursion of about 0.7 volt. During the continuation of 

 the reaction the potential exhibits irregular rhythmical fluctuations 

 about this point; later, as the reaction begins to decline, it decreases 

 by degrees, finally swinging back rather abruptly to zero and a little 

 beyond as the reaction ceases. It is characteristic that immediately 

 after repassivation the wire is always slightly more positive than be- 

 fore, by a potential of 0.01 to 0.02 volt, and remains in this condition 

 for some time; by degrees, especially if the acid is stirred, the wire 

 resumes its original potential. The rhythmic variation of potential 

 is an especially interesting peculiarity from the biological point of 

 view, since rhythmicity of a similar kind is frequent in irritable living 

 tissues, as well as in other film-covered inorganic systems, such as 

 mercury in hydrogen peroxide. It indicates a tendency in the early 

 stages of the reaction to an alternating formation and disruption of 

 the passivating film ; later the process of formation predominates and 

 the film becomes continuous over the whole surface; the wire is then 

 passive. The " af ter-positivity" has an analogy to the so called "posi- 

 tive after- variation" observed under certain conditions in nerves after 

 stimulation ;i^ from the most general point of view it is to be regarded 

 as a polarization effect of the kind found at all polarizable electrodes. 

 Time Relations of Recovery of Transmissivity. — The behavior of a 

 wire in nitric acid of 60 per cent concentration will first be described 

 for illustration. When such a wire, after having been left undis- 

 turbed in this solution for some time {e.g. an hour) , is touched at one 

 end with zinc a wave of activation sweeps rapidly (at some hundred 

 centimeters a second) over its whole length; after 1 or 2 seconds the 

 reaction ceases and the metal becomes again passive. For some 

 minutes after repassivation the wire is found to be incapable of 

 transmitting activation for more than a limited distance. At the 

 very first, touching with zinc produces only a slight local reaction; 

 when touched 30 seconds later the local effervescence and darkening 

 caused by the zinc are somewhat more pronounced, and the reaction 

 spreads slowly for 2 or 3 cm. from the contact; after 1 minute there 

 is somewhat more rapid transmission through 4 or 5 cm.; after 2 



^^ Tigerstedt, C, and Donner, S., Skand. Arch. Physiol., 1913, xxx, 309. 



