It is generally recognized by clinicians and physicists alike that the graphic apparatus in current use for recording the form of the pulse beat introduces considerable inaccuracy. It is therefore of general importance to recognize that we possess in the segment capsules of Frank a form of recording apparatus that may be trusted to reproduce faithfully the pressure and volume changes actually existing in the veins and arteries and, in addition, one which is adapted to record directly the apex beat and heart sounds. The use of this valuable apparatus has received little encouragement from clinicians and physicians, partly because the details of its operation are not sufficiently understood, and, partly, because it has not been available for bedside work. It seems desirable therefore to describe briefly, yet accurately, the principle and operation of these capsules and an arrangement which makes their use at the bedside practical in hospital wards.