Page:Collected Physical Papers.djvu/273

 XVIII ON THE SIMILARITY OF EFFECT OF ELECTRICAL STIMULUS ON INORGANIC AND LIVING SUBSTANCES

In working with receivers for electric waves, I found that under continuous stimulation by the oncoming message, the sensitiveness of the metallic detector disappeared. But after a sufficient period of rest it regained once more its normal sensitiveness. In taking records of successive responses, I was surprised to find that they were very similar to those exhibiting fatigue in the animal muscle. And just as animal tissue, after a period of rest, recovers its activity, so did the inorganic receiver recover after an interval of rest.

Thinking that prolonged rest would make the receiver even more sensitive, I laid it aside for several days and was astonished to find that it had become inert. A strong electric shock now stirred it up into readiness for response. Two opposite treatments are thus indicated for fatigue from overwork, and for inertness from long passivity.

A muscle-curve registers the history of the fundamental molecular change produced by excitation in a living tissue, exactly as the curve of molecular reaction registers an analogous change in an inorganic substance. The two represent the same thing; in the latter the molecular upset is evidenced by the change of conductivity, while in the former it is manifested by the change of form. We have thus means of studying molecular reaction produced by stimulus of varying frequency, intensity and duration. An abyss separates