It is now generally recognized that to understand properly the action of the heart it is necessary to employ mechanical instruments which register for comparison the simultaneous events in its various chambers.
For the recording of events in the cardiac cycle two types of instruments have been devised : one, for recording the ventricular contraction, depends on the application to the artery at the wrist of a metal piece or knob of a tambour ; the other depends on the application of a rubber cuff or armlet encircling the arm, attached to which is a hollow rubber ball of sufficient resilience to transmit the variations of pressure to the air within a surrounding glass sphere connected with a writing tambour. By this latter method, and a careful regulation of the pressure within the closed system so that it shall be maintained at a constant level between the diastolic
HALSEY RH. AN ADAPTATION OF THE ERLANGER CAPSULE TO ANY POLYGRAPH FOR OBTAINING . ARTERIAL PULSE RECORDS. Arch Intern Med (Chic). 1916;XVII(4):540-542. doi:10.1001/archinte.1916.00080100084008