“…During the early part of the century, when artificial pneumothorax was widely used as a therapeutic measure, there was considerable interest in its physiological effects. Studies in animals (Bruns, 1913;Adams and Morris, 1921 ;Weiss, 1926;and Moore, 1931) showed that shortly after induction of a pneumothorax there was a considerable fall in arterial oxygen saturation which returned to normal a few hours later. This, in the absence of a change in total ventilation, was thought to be due to an initial shunt of blood through the collapsed lung which gradually lessened due to pulmonary vasoconstriction.…”