Welch produced oedema of the lungs experimentally by increasing the pressure in the pulmonary vessels by ligature of the aorta and its branches, but this raised the blood pressure only about one-tenth of an atmosphere, while in some of Loeb's experiments the osmotic pressure, due to retained metabolic products, was equal to over thirty atmospheres.
In large vessels it is usual to pass a ligature round the vessel and tie it with a reef-knot.
Apply the ligature, if possible, at the bleeding point, tying both ends of the cut vessel.
Haemorrhage has been classified as - (I) primary, occurring at the time of the injury; (2) reactionary, or within twenty-four hours of the accident, during the stage of reaction; (3) secondary, occurring at a later period and caused by faulty application of a ligature or septic condition of the wound.
Apply a ligature above, not on the top of, the situation of the bite, twist the string tightly with a stick.