Observation of changes in volume of a congested limb as a means of studying the behaviour of capacity vessels.

1. Experiments have been performed to determine whether the volume of a forearm congested by a cuff inflated to a low pressure (15-30 mm Hg) reflects active changes in the vascular capacity of the part while remaining relatively insensitive to the passive effects of changes in perfusion.2. Conditions were chosen in which existing evidence suggests that blood flow and capacity vary independently of each other.3. The results of these experiments suggested that active changes in capacity can be studied by the continuous observation of the volume of a congested limb, provided that the associated change in blood flow is a reduction from the basal level and is not an increase above the basal level.