Myxedema is characterized by a mucinous edema of connective tissues including the skin. The chemistry and physical properties of the mesenchymal fluids such as the synovia,9 the fluids of the eye,7 and the inner ear,8 as well as of connective tissue ground substance10 are changed. The acid mucopolysaccharides, preferably hyaluronic acid, determines the mucinous character of all mesenchymal fluids. Hyaluronic acid has a strong water-binding capacity. It keeps the water content of the mentioned fluids and the skin. The substance is contained in the cytoplasmic granules of mast cells, and the release takes place as a degranulation.4 A physiologic degranulation of mast cells may be brought about by an extracellular edema. If the increase of tissue water is just moderate, only few granules are extruded; if intense, a complete degranulation may take place. In leaving the cell, the substance does not maintain the morphologic character of