“It was first sought to obtain information upon this subject by investigating the manner and extent to which the action of the heart is affected by obstruction of the renal arteries and the other large branches of the aorta; the facts obtained by taking this line of inquiry were not however of a kind fitted to throw light upon the problem which it was specially desired to solve. It soon became evident that an investigation of the manner in which the renal secretion and circulation are nominally regulated, and the relation which these bear to the regulating mechanism of the systemic circulation, would be best fitted to supply information of the kind required. The method employed, was to record graphically the changes in volume of one or both kidneys, while at the same time the changes in the blood-pressure in the aorta and the rapidity with which the urine was secreted were also recorded on the same revolving cylinder or, as continuous tracings, upon the paper of Ludwig’s kymograph. The method used for recording the changes in volume of the kidney is the same in principle as that of the plethysmograph. The kidney is enclosed in a rigid metal box, the arrangement being such that while the organ can freely expand or contract, and while the changes in volume are recorded by a lever writing with a light glass pen upon the kymograph paper, no obstruction is offered to the entrance and exit of blood by the renal vessels nor to the outflow of urine by the ureter. The kidney is surrounded by warm olive oil, which, however, is not in immediate contact with its surface, but is separated from it by a delicate flexible membrane of a kind which has already been referred to by the author in several of his published papers, and which prevents any escape of the oil by the side of the blood-vessels and other structures entering the hilus of the gland.… When the instrument is in use, the kidney lies between two delicate, exceedingly flexible membranes, which apply themselves closely to its surface and to the surface of the structures entering the hilus of the organ, and each of these membranes forms with each of the symmetrical halves of the box a chamber which is filled with oil and which communicates by a relatively wide flexible tube with the recording instrument.”