. Elements of human physiology. Physiology. 194 PHYSIOLOGY that the manometer is put into connection with the artery. The clip is then talien oE tlie artery. Tlie column of mercury drops to about 120 mm. (if the carotid of the dog is the artery used), and stops at about that level, rising and falling slightly with every heart-beat. The object of using sodium sulphate or magnesium sulphate solution is to delay clotting in the cannula. On investigating in a similar manner the condition of the veins, we find quite a different state of things. If a vein be ligatured in any part of its course, it s
. Elements of human physiology. Physiology. 194 PHYSIOLOGY that the manometer is put into connection with the artery. The clip is then talien oE tlie artery. Tlie column of mercury drops to about 120 mm. (if the carotid of the dog is the artery used), and stops at about that level, rising and falling slightly with every heart-beat. The object of using sodium sulphate or magnesium sulphate solution is to delay clotting in the cannula. On investigating in a similar manner the condition of the veins, we find quite a different state of things. If a vein be ligatured in any part of its course, it swells up on the distal side and shrinks on the side towards the heart. If it be cut across, the bleeding that occurs takes place nearly entirely from the distal end. The haemorrhage moreover is of a different character from that which occurs when an artery is Fig. 98,. Blood-pressure tracing taken with mercurial manometer (from carotid of rabbit). A, abscissa or line of no pressure. divided. The blood, instead of spui'ting out to a distance, wells up and is not increased or in any way affected by the heart-beat. If we connect a manometer with a vein, we find that the pressure amounts to a few mm. of mercury. Thus we see that the blood, which in the arteries is under high pressure and has an intermittent flow, by the time it has reached the veins is at a low pressure, and the flow has lost its intermittent character. What is the cause of this change in the character of the flow? The blood in passing from arteries to veins has to traverse the arterioles and capillaries and in so doing meets with considerable resistance owing to the friction between the blood and the vessel-walls. Every time an artery divides, although each separate branch is smaller than the original branch from which it springs, the united sectional area of the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance o
Size: 1508px × 1656px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectphysiology, bookyear1
