Kymograph, London, England, 1925-1935 The kymograph is a classic
tool of laboratory research invented by the German physiologist
Carl Ludwig (1816-1895) in 1847. It was first used to measure
blood pressure during physiological experiments. A cannula
connected to a U-shaped tube filled with mercury was inserted
into the artery of an animal. On top of the mercury was a float
attached to a pen. As the blood pulsated, the pen recorded the
movement on smoked paper wrapped around the metal drum. The
kymograph, shown here, is adapted to record muscle contractions.
An isolated muscle is placed on coils of wire and connected to
an electrical stimulus, controlled by a switch. The muscle is
also attached to the kymograph to record when the muscle
contracts. When the muscle is stimulated, heat is produced and
transferred to the thermocouple (cut away to show the two coils
of metal which, when heated, produce an electric current). The
thermocouple is attached to a galvanometer to record the
electric current produced when