Sir Clifford Allbutt says (in _Diseases of the Arteries_, vol. i, p. 92): “It is in the experience of us all that, as the walls of the great vessels lose their elasticity, the systolic pressure mounts above its proportion to the diastolic which falls. In aortic regurgitation the difference between the systolic and diastolic figures may be enormous, as much as 105 mm. to 210 mm. In a certain ‘Adams Stokes’ case of my own, at a pulse rate of 32, the systolic pressure was 180, the diastolic 90 mm. Thus, with the difference between the two pressures waxing as the resilience wanes, the blood pressure moves more suddenly and largely, bangs more, and thus racks the machinery. The greater vaso-motor lability in youth has a like effect, but the vessels are then much more resilient and energy is stored. In an early hyperpietic, or nephritic subject the systolic exorbitancy may be considerable or variable, while the diastolic is steadily in excess. As age advances the amplitude increases to 80 and upwards; a systolic pressure of 160 mm. may be associated with a diastolic of 75 mm. or 80 mm.” Dr. H. C. Mann says: “That as compensation fails, the diastolic pressure begins to fall, and the systolic becomes irregular.” It must seem very difficult for a beginner, or even for an experienced busy practitioner, to find his way through all these devious by-paths, which must look to him often to be blind alleys and to lead nowhere, but out of the welter a few good and sound working principles emerge. “_Firstly_, that at middle age and afterwards the knowledge of an habitual systolic pressure is of first-rate importance. “_Secondly_, that this knowledge can be confirmed and sometimes rectified by knowledge of the diastolic pressure (manifest valvular diseases of the heart, especially aortic regurgitation, are excluded); and that a continuous rise of systolic and diastolic pressure point conclusively to threatening or confirmed arterio-sclerosis. “_Thirdly_, that a steady ratio between the two pressures, even when much above normal, is a sign that the heart is doing its work well; and conversely, a falling diastolic ratio is a sign of failing compensation.” Dr. Louis M. Warfield, in his work on Arterio-Sclerosis, says: “It is most important to estimate accurately the diastolic pressure as well as the systolic, for only in this way can we obtain any data of value regarding the driving power of the heart and the condition of the vaso-motor. A high systolic pressure does not necessarily mean that a great deal of blood is forced into the capillaries. Actually it may mean that very little blood enters the periphery. The heart wastes its strength in dilating constricted vessels without carrying on the circulation adequately. The pulse pressure is the difference between the systolic and diastolic pressure, and practically represents the heart lode.” All these considerations demonstrate the importance of watching closely the pump as well as the pipes.