Marey's description of the illustration taken from the English edition of his book, The Animal Machine, Terrestrial and Aerial Locomotion, 1873, "...Although, to all appearance, the animal is dead, it will nevertheless retain for several hours the circulation of the blood, and the power of motion under the influence of electric discharges. An electric excitator conveys the current from an induction coil to the nerve of the frog. In order to register these movements and to depict them by curves which express their different phases, they are transmitted to the myograph in the manner already described. The tendon of the muscle is cut, and connected by a wire which is fastened at the other end to the lever of the registering apparatus; the latter moves in a horizontal plane, when the contractile force of the muscle is exerted upon it. As soon as the muscle cease to act, the lever returns, under the pressure of a spring, to its original position. At the free extremity of the lever is a point which traces, on a turning cylinder covered with smoke paper, the motions produced by the alternate contraction and relaxation of the muscle."