The process o f calcification is depend­ ent on the formation of a protein mat­ rix. This matrix serves as the ground substance within which the mineral salts are deposited. The failure to calcify in these experiments appears to be largely the result of inadequate matrix synthesis. Disturbances in deposition of dentin were noted in the experimental animals. The dentin in the incisors which was de­ posited during the deficiency period ap­ peared to be hypocalcified, as character­ ized by an increase in the number of calcospherites. With no apparent change in the mineral intake or metabolism, the changes in the dentin must be reflected in the depolymerization of the ground sub­ stance and in failure to form a suitable protein matrix. The degenerative lesions in bone and incisors were found to be reversible when lysine was added to the diet after seven weeks of deficiency. The structures of the long bones resumed their activity as evi­ denced by the accelerated thickening of the epiphyseal plate and trabeculae. The alveolar bone also reverted to a normal appearing structure.