The escape of a vital dye from the lymphatics of the ears of living mice and its subsequent movement through normal and pathological connective tissue have been observed at high magnification. The dye first appears outside such channels as bristly, wavy lines of color, which can be bent and twisted by pressure with a micro probe and spring back to their original positions when the pressure is removed, as if the dye were fixed upon or between some tissue elements. Our findings indicate that this is the case, that the bristly lines of color are formed by dye moving between connective tissue fibers or along them. With the onset of mild edema, such as the dye induces secondarily, the bristles disappear, the coloration becoming diffuse and freely movable with the micro probe.

When edema is induced before dye is introduced into the lymphatics, the character of its escape is wholly different. It first appears as a colored cloud, freely movable in the edema fluid, the manner of its passage into the tissues being completely changed.

In the ears of mice partly dehydrated by bleeding, or in those of dead animals, the bristly or wavy lines were more evident than in normal individuals. It was plain that dehydration did not change the mode of transportation of the dye through the tissue but merely emphasized some of the characteristics of its passage. In animals injected intravenously with large amounts of physiological saline, with result in the presence of more tissue fluid than usual, the colored bristles were seldom seen.

It is plain that connective tissue fibers serve indirectly as pathways for the transport of substances of large molecule.

We have not been able by the dye method to demonstrate the presence of any free fluid in the normal tissues of the mouse ear.

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