It is evident that a lotion containing mineral acid will dissolve out the earthy bases of bone-tissue and quicken disintegration, and for this purpose it has been applied to some extent in surgery. Chassaignac recommended dilute hydrochloric acid, but more recently Mr. Pollock has brought forward much evidence in favor of the application of sulphuric acid mixed with an equal part of water, "for the more speedy removal of dying bone, or more rapid separation of dead portions, or destruction of the surface of carious cavities;" he finds it simple and safe, and comparatively painless - nor has he ever seen bad consequences from it. His first case, one of necrosis of cranial bone, was touched daily with the dilute acid, - the diseased part quickly separated, and healthy granulations formed. Cavities may be filled with lint soaked in acid, and, when this is removed, in two or three days an opaque white layer may be seen and taken away; this is a slough, soft owing to removal of earthy particles, which may be found lying loose in the wound: any pain caused by the caustic ceases in a short time because the acid is soon neutralized. In some flat bones, such as those of the trunk or pelvis, the undiluted acid may be cautiously used. Recovery may be secured "in weeks instead of months" under such treatment, though it will not always succeed without operative interference (Lancet, i., 1870). W. Hayward, H. Marsh, and others, have also recorded good results from the practice recommended by Mr. Pollock.