Whether in the academic or the medical world, electricity and animal magnetism shared a similar and interdependent history, a history that shows the limits of absolute categorizations and demonstrates the necessity of redefining borders in light of controversies and events. These borders were, by definition, points of tension and opposition, as well as places requiring negotiation and exchange. Considering only those personalities mentioned in the article by Sutton devoted to medical electricity and animal magnetism, the strict opposition between inclusion and exclusion is inadequate. Indeed, the process of the classification of knowledge is not linear, nor is it a preserve of official Parisian institutions. The medical field, itself, was not restricted to scholarly disputes; it had to take into account commercial and professional dynamics as well. Depending on the different points of view and the issues, the demarcation of knowledge, of personalities, and of legitimate practices are not identical. Such a fluid border characterized the margins of medicine in which Mesmer and the Mesmerists evolved.