Careful estimation of the blood pressure in surgical cases has, at times, great value. In all surgical diseases the most important fact to know is not the systolic pressure, but the pulse pressure. If the pulse pressure keeps within the range of normal, does not drop much below 30 mm. in an adult, then so far as we can tell the circulation is being carried on. When the systolic pressure is gradually falling and the diastolic remains the same, the circulation is failing and unless the pulse pressure can be established again the patient will die. Again we see the value of the pulse pressure. All prolonged febrile diseases tend to produce a lowering of the blood pressure picture. The diastolic does not fall to the same extent as the systolic so that there is a pulse pressure smaller than normal. This is to be expected from what we know of the general depression of the circulation in fevers. The blood pressure reading is only a graphic record of what we have long known, and enables us from day to day accurately to measure the general circulation. =Head Injuries= It was claimed that in fracture of the skull or in concussion much could be gained by frequent estimations of the blood pressure. This seemed probable in the light of experiments on compressing the brains of dogs by the use of bags inserted through trephine openings (Cushing). In the clinic, however, it has not been found of any material value. It has a value in differentiating a simple fracture, let us say, from a case of uremia which is picked up on the street with a bump on the head. There the high pressure usually found would at once direct attention to the kidneys and the newer methods of blood examination would at once settle the question. Naturally uremics may also have skull fracture. There the diagnosis would be complicated. A decompression done at once would be indicated. If the skull fracture happened in a uremic, the decompression would probably do no harm. In fact, there are some who advise decompression for uremia. =Shock and Hemorrhage= In shock the blood pressure picture is low but the pulse pressure drops to abnormally low figures. It seems to me that the blood pressure instrument has its greatest value in surgery in the warning it gives to the operating surgeon in cases of impending shock.