“That the work of the kidney is to an unusual degree dependent on the flow of blood through it seems suggested by the vascular arrangements; for these are extremely favourable to a full and rapid stream of blood through the organ. The short and relatively broad renal artery comes off direct from the abdominal aorta, where the blood-pressure is extremely high; the renal vein opens directly into the vena cava, where the blood-pressure is extremely low. Between the mouth of the renal artery and the mouth of the renal vein the difference of pressure is very great indeed; and as we have seen in treating of the vascular system it is the difference of pressure between two points of the vascular tract which is the actual cause of the flow of blood from the one point to the other. The difference of pressure indeed which drives the blood through the limited area of the kidney is the same difference of pressure which drives the blood along the abdominal aorta down to the foot and back again to the vena cava.”