“Beclard was the first who endeavored to prove that in the muscles of man heat may be substituted for mechanical work, and vice versa. For this purpose he examined the thermometrical temperature of two muscles, both of which contracted, but one worked, that is to say, raised weights, while the other did not work. It might have been expected that less heat would have been found in the first muscle, because a portion of the heat produced during its contraction ought to have been transformed into work. The idea which governed Beclard’s experiments was assuredly correct, but the means at his disposal for ascertaining the heating of the muscles were altogether insufficient. A thermometer was applied to the skin at the level of the muscle, in order to give the measure of the heat produced; thus the variations of temperature obtained by Beclard according as the muscle worked or not, were so slight that no real value could be attached to them.”

— Etienne Marey (1873), Animal Mechanism (pg. 17)

“Beclard was probably the first to attempt to measure the relation of quantity and of transformation, thermodynamically, if such energy-transformations actually occur, in the animal machine.”

— Robert Thurston (1894), The Animal as a Machine and Primer Mover (pg. 41)