Distinguishing lymphatics from blood vessels in normal and diseased skin.

If it were true that lymphatics are essential for the removal of macromolecules and in this way the oncotic and hydrostatic pressures within the interstitium are determined; if it were true that lymphatics are the principal pathway for the exit of antigen and of macrophages and hence, important for cell mediated immunity, then on both accounts the lymphatics are of great significance. There must be some anxiety that none of this can be confirmed and that some tissues such as the brain and the eye do not need lymphatic vessels as such. We must also note that in many diseases the lymphatic system seems to be severely disrupted, and yet it is difficult to show that the tissues are severely compromised. One wonders to what extent blood vessels or any other system, such as the mononuclear phagocytic system, can take over the role of the lymphatic. To answer these questions one needs to be able to identify the lymph clearance system as distinct from the blood supply system. Although this is easy in health, it becomes very difficult in disease.