Vital dyes injected intradermally enter lymphatic capillaries directly, rendering them visible, and appear later in the draining lymphatic trunks as colored streamers. The method enables one to perceive the state of the lymphatic channels and the rate of lymph flow within them. It yields consistent results when tested under physiological conditions known to increase or decrease lymph flow.

In the horizontally placed normal limb at rest there is slight lymph flow. In a normal leg or arm hanging downward lymph flow ceases although fluid in the limb increases. When a previously dependent arm is raised above the head, or when the foot of a seated subject is propped on a table, lymph flow in the raised limb becomes active. It ceases in the skin of an arm subjected to partial obstruction of the veins by pressure from without, but very active lymph flow appears during the reactive hyperemia which follows upon the release of venous obstruction. It is still greater following release of total circulatory obstruction, and seems to be the same whether or not the limb has previously been engorged with blood. In the ischemic patches which appear in the skin of a limb during total circulatory obstruction (Bier's spots) the lymphatic capillaries are definitely and considerably constricted, whereas they are slightly dilated in the purple, congested regions of the skin round about. On release of obstruction there occurs a strikingly rapid, equal lymphatic drainage from both regions.

The significance of all the findings is discussed.

When dye is injected intradermally and the skin sucked, much of the foreign material is driven into the lymphatics draining the injected area.

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