The primary morphologic effects of vitamin C deficiency occur in the intercellular substances of certain mesenchymal derivatives. These can best be described in terms of the prototype of these structures, loose connective tissue. Under normal conditions the type cell, the fibroblast, lies in an amorphous ground substance within which fibrils (reticulum) are formed which may in turn become gathered into wavy bands of collagen. In this transformation the fibrils seem to become cemented together by a translucent matrix, the formation suggesting a colloid phenomenon, the setting of a gel. It is precisely this phase of the formation of intercellular materials which may be completely controlled by vitamin C. Thus in guinea pigs which have been depleted of vitamin C the ground substance and fibroblasts are present as in health but fibrils or collagen are not formed. When the deficiency is satisfied, translucent bundles and masses of collagenous materials reappear within