The velocity of lymph flow in the canine thoracic duct

1. The velocity and pattern of movement of lymph in the thoracic duct of anaesthetized and conscious dogs has been studied by observing the movement of droplets of ultrafluid lipiodol in the duct.2. The velocity of flow when anaesthetized varied from 0.1-2.0 cm/sec, to 5.0 cm/sec when conscious.3. The pattern of flow was affected by respiration and the cardiac cycle. Most movement occurred at the end of inspiration.4. The duct of five autopsy preparations was perfused with saline to assess the volume and velocity of flow produced by the level of pressure gradients previously observed in the duct. These studies show that the small gradients (2-5 mmHg) observed during life are more than sufficient to produce the normal volume and velocity of flow measured. The mean resistance of the duct was 0.5 mmHg/ml. min.