Fig. 3. Dynamic sequence of events of in vivo  gas embolism in (A ) control and (B ) surfactant-pretreated animals. In both cases, numbers represent (1) initial air entrapment, (2) embolism constriction, and (3) breakup into smaller bubbles. Control case (average initial embolism diameter = 66 μm; scale bar = 700 μm) (A ) shows only very local constriction, whereas surfactant case (average initial embolism diameter = 58 μm; scale bar = 450 μm) (B ) demonstrates overall constriction and bubble breakup.