. Elements of human physiology. Physiology. 204 PHYSIOLOGY possessing two vertical side tubes c and d, the pressure at c will be greater than that at d, since at c the momentum of the moving mass of blood is added to the lateral pressure of the fluid. A tube of this shape is connected with an artery, such as the carotid, and the tubes h and h' are attached at the points c and d. These two tubes are united at their upper extremities. In this case, so long as the blood flows from a to b, the fluid in h will rise higher than in h', and the difference in height of the fluid in the two tubes will b
. Elements of human physiology. Physiology. 204 PHYSIOLOGY possessing two vertical side tubes c and d, the pressure at c will be greater than that at d, since at c the momentum of the moving mass of blood is added to the lateral pressure of the fluid. A tube of this shape is connected with an artery, such as the carotid, and the tubes h and h' are attached at the points c and d. These two tubes are united at their upper extremities. In this case, so long as the blood flows from a to b, the fluid in h will rise higher than in h', and the difference in height of the fluid in the two tubes will be proportional to the velocity of the blood. A graphic record of this difference of pressure is obtained by allowing a narrow beam of light to throw an image of the menisci of the two columns of fluid through a slit on to a moving photographic plate. Such a record is given in Fig. 107. The width of the black space at any point is proportional to the velocity of the blood at the moment at which this part of the record was being taken. Of course this instrument has to be calibrated if we wish to determine the velocity of the blood in absolute measure. In Fig. Eecord of blood-velocity in the carotid artery of the rabbit. (Cybulski.) Fig. 107 the velocity at the point 1 and 1', corresponding to the cardiac systole, was 248 mm. per second. At 2 and 2', corresponding to the dicrotic elevation, the velocity was also 248 mm. At 3 and 3', towards the end of diastole, the velocity sank to 127 mm. The rate of flow in the capillaries may be measured by direct observation of the rate at which a blood-corpuscle moves along a capillary of the frog's web. It probably varies from ^ to 1 mm. per second. The area of the large veins near the heart (under normal pressure) is equal to about twice that of the arteries, and this relationship between veins and arteries holds good for the entire system. Hence, since the same amount of blood enters the heart as leaves it at each beat, the rate of f
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