Trypan blue injected into the circulating blood stream of frogs accumulates rapidly in an inflamed area.
When trypan blue is injected directly into the area of inflammation it is fixed in situ and fails to diffuse outward.
If the dye is injected at the periphery of an inflamed area it fails to enter the site of inflammation. This failure of penetration is caused by the occlusion of lymphatic vessels and the presence of a network of fibrin in the inflamed area.
These experiments furnish additional evidence that fixation of foreign substances by the inflammatory reaction is due to mechanical obstruction caused by a network of fibrin and by thrombosed lymphatics at the site of inflammation.