FAIL-SAFE FROG: To demonstrate in vivo “negative variation”—known today as a nerve signal, nerve impulse, or action potential—Emil du Bois-Reymond would secure a frog in a clamp and slice an opening in its back to access the spinal cord. He would then insert metal electrodes to stimulate whole-body tetanus, a prolonged muscle contraction, by discharging an electrical current to the central nervous system. Strips of wet blotting paper draped over the frog’s body served as the electrodes connecting the frog to a saline pool below, which was linked to a galvanometer that recorded the expected change in current. “This is not some trace observance that has to be descried amidst ambiguous conditions and cases of failure,” du Bois-Reymond wrote in the second volume of his treatise on electrophysiology, first published in 1849; “no, this is about a needle moving forty to seventy degrees, about an experiment so simple, striking, and secure in its success that, as long as I have apparatus and frogs, I volunteer to repeat it at any time, at any place, as often as desired, without it ever failing.” MAX PLANCK INSTITUTE FOR THE HISTORY OF SCIENCE; (inset) COURTESY OF GABRIEL FINKELSTEINIn 1841, German physiologist and anatomist Johannes Müller handed his student, Emil du Bois-Reymond, a research report that would change the course of his career. It was an essay by young Italian physicist Carlo Matteuci, summarizing his work using electricity to probe living organisms—namely frogs, the species of choice for most early electrophysiologists. Du Bois-Reymond “knew how to do physical experiments with electricity,” says historian Gabriel Finkelstein of the University of Colorado Denver, and the idea of applying his skills to study life called to him.
Tasked with replicating and expanding Matteuci’s work, du Bois-Reymond sought to improve upon his contemporary’s techniques. He discovered that the use of blotting paper soaked in a simple saline solution could prevent contact electricity, small currents generated by organic tissue when in contact with a metal electrode. “Those currents were artifacts of the apparatus, and they masked or confused any attempt to detect electricity in organic tissue,” says Finkelstein. Du Bois-Reymond also developed electrodes made of modeling clay, zinc, and zinc sulfate that didn’t require immersion in a buffer. But perhaps his most notable innovation was in the instrument he built to better measure the signals detected by the electrodes.
Like Matteuci, du Bois-Reymond used an electromechanical instrument known as a galvanometer, which has a ...
