. Elements of human physiology. Physiology. THE VASCULAR MECHANISM 193 artery, the animal is injured by the loss of the blood which is necessary to fill the tube, and the experiment is soon stopped by the clotting of the blood in the tube. There are many different forms of manometer. The best for investigating changes in the mean arterial blood-pressure is Ludwig's mercurial manometer. This instrument consists essentially of a U-tube with two vertical limbs about eighteen inches long. This is half filled with clean mercury. On the surface of the mercury in one limb is a float, from which a sti
. Elements of human physiology. Physiology. THE VASCULAR MECHANISM 193 artery, the animal is injured by the loss of the blood which is necessary to fill the tube, and the experiment is soon stopped by the clotting of the blood in the tube. There are many different forms of manometer. The best for investigating changes in the mean arterial blood-pressure is Ludwig's mercurial manometer. This instrument consists essentially of a U-tube with two vertical limbs about eighteen inches long. This is half filled with clean mercury. On the surface of the mercury in one limb is a float, from which a stiff fine rod (of steel or glass) rises, bearing on its upper end a writing point. This point is adjusted so as to record its movements by scratching a white line on the smoked paper of a kymograph. (A kymograph is merely an arrangement of revolving Fig. Arrangement of apparatus for taking blood-pressure tracing, a, artery (carotid); c, cannula; d, three-way cock; m, mercurial manometer ; b, drum covered with smoked paper. cylinders, moved by clockwork or other means, arranged to carry a roll of smoked paper.) Instead of using the smoked paper, a pen may be fitted to the end of the vertical rod, and its excursions recorded in ink on a moving band of white paper. The other limb of the manometer is connected by a flexible rigid tube (such as lead) with a small tube or cminula, which is tied into the central end of the artery. While the cannula is being tied, a clip is placed on the artery at (a), so as to prevent the blood escaping. At (d) there is a three-way cock. This is first turned so as to put the tube (x) into connection with the tube to the cannula, and the whole is then filled with a half-saturated solution of sodium sulphate, or a 25 per cent, solution of magnesium sulphate. The cock is then turned and the tube leading to the manometer filled in the same way Both tubes being full, the solution is injected forcibly into (x), so as to raise the column of mercury about
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