The hydrogel that surrounds cells in soft tissues. It is a mucopolysaccaride starch gel, and the serum that leaves the blood capillaries flows through this gel, some to return to the exiting venous blood, some to enter the lymph system. There is an old medical axiom: the blood feeds the lymph, and the lymph feeds the cells. Interstitial fluid that flows through the starch colloid is this lymph.