The discoloration of white rat hair by acid preparations has been employed as a model reflecting local tissue destruction by intravital fixation as contrasted to tissue dissolution. Nitrate reduction products in equilibrium with nitrite ion in moderately strong acid result in much more rapid tissue fixation than is accomplished by acid preparations alone. Parallel differences were found in the color reaction of normal skin to different acid preparations. The rapid fixing capacity demonstrated by these models may be useful for sharply localized destruction of topical lesions clinically.