Dr. Chas. Truman suggests a mixture of iodoform and arsen-ious acid as a painless devitalizer under all conditions. It is applied as follows: After placing the rubber dam in position, drying cavity, etc., the amount of the arsenious acid it is proposed to employ is placed upon a glass slide and an equal quantity of iodoform, or an excess is added and a paste made with a five per cent. solution of carbolic acid, and the whole carried to the pulp on a piece of cotton, the size of a pin's head. This is then covered with a gutta percha cap, or one of platinum, and a temporary filling introduced; the latter may consist of softened gutta percha or zinc filling material. Pressure upon the pulp must be avoided.

Some prefer to wound the pulp, so as to draw blood, before the application of the arsenical preparation is made, and thus insure its speedy action. Care is necessary that the arsenic should be completely secured in the carious cavity, and no portion of it come in contact with the parts outside of the tooth. In the case of proximal cavities, a roll of bibulous paper, saturated with sandarach varnish, may be pressed between the teeth, beyond the cavity, and thus prevent the arsenical preparation from coming in contact with the gum and cheek, or gutta percha may be softened and packed against the margin of the gum in such a quantity as will fill the interspace. Failure to observe such precautions may result in violent inflammation involving the alveoli and causing necrosis of the bone. After the devitalization of the pulp has been accomplished, it is necessary that every particle of the arsenic should be removed from the tooth. The effect of permitting the agent to remain in the tooth for a longer time than is necessary for the devitalization of the pulp only, is peridental inflammation. Where several applications of the arsenical preparation fail to produce the desired devitalization, the resistance thus offered to the influence of the agent may be owing to several causes; a granulated, protective covering, which is formed over the surface of the exposed portion of the pulp, which defends it from the action of the arsenic; or, extraordinary vital power in the pulp, which may be due to the peculiar constitution of the patient, who probably would not be as susceptible to the action of arsenic as the majority of persons are, even if it were administered by the mouth.

Such resistance to the action of the devitalizing agent may be overcome either by the removal of the granulated surface where it exists, or, in cases of non-susceptibility, by puncturing the pulp with a pointed instrument, charged with the arsenical preparation; first taking the precaution to obtund the sensibility of the organ by the application of a benumbing agent. The action of arsenic depends upon both local and systemic conditions. When the capillaries of the pulp are congested as a result of the inflammation, the absorption of the agent is prevented or retarded, and it acts chemically upon the superficial tissue of the exposed portion of the pulp and causes pain, rendering it necessary to relieve the congestion before the nerve tissue can be primarily affected. In case of a lymphatic temperament, characterized by low vital power and excess of fluids in the tissues, the arsenic is readily absorbed and devitalization speedily results; whereas in cases where there is great nerve-power or excessive nervous irritability, the susceptibility of the tissues to its influence is very feeble, and the devitalization of the pulp is difficult and sometimes impossible, unless repeated applications are made.

It is not considered advisable to apply arsenious acid to a dental pulp in an acute stage of inflammation, and the method generally pursued in such cases is to remove the loose matter in the cavity, first applying the rubber dam, and relieve the congestion by slightly puncturing the pulp so as to cause a slight hemorrhage. Then apply an anodyne, such as oil of cassia, oil of cloves, eugenol, terpinol, or other agent of like properties. This should be carefully sealed in the cavity, without pressure being made upon the pulp, for from one to three days, according to the degree of inflammation existing in the parts. At the expiration of such time, the dressing is removed, and if the inflammation has subsided, as is shown by the symptoms presented during the period the dressing has remained in the tooth, an application of arsenious acid may be made. Upon the removal of the arsenic, an application of tannin and glycerin should be made in order to harden the devitalized pulp and render its removal easy in the form of an entire mass; then apply some efficient antiseptic dressing to pulp-canal, first washing out with peroxide of hydrogen. The use of dialyzed iron is also recommended, after the removal of the arsenic, as it is not always certain that the latter agent has been carefully applied. The dialyzed iron is introduced into the cavity on a piece of wood. The cavity should be kept free of moisture from the time of the application of the arsenic up to the time of the application of the dialyzed iron.

When arsenious acid is applied to the surface of an exposed pulp, its first effect is stimulating, followed by paralysis of the sensory nerves, inflammation being excited the degree of which depends upon the quantity of arsenious acid employed. After the stimulating effect passes off the arsenic is gradually absorbed and the pulp slowly dies. Too large a quantity of the arsenic will cause violent inflammatory action, increase the congestion and prevent the pulp from absorbing the agent; and experience has shown that recently exposed pulps are more readily devitalized by arsenious acid than those which have been exposed for a considerable time. It is therefore advisable to employ minute quantities of arsenic as a devitalizing agent, and to avoid pressure on the pulp when applying it, so that the pain occasioned by its action may be limited to the space of one hour on an average. The danger of an excess of arsenic passing through the apical foramen of the root to the peridental membrane must always be guarded against by carefully regulating the quantity of the agent; on the other hand all extraneous matters that will interfere with the action and application of the arsenic to the exposed surface of the pulp must be removed, or irritation and pain and not devitalization will result. For the application of arsenious acid to the surface of a fractured tooth, where it is difficult to retain it, the filling may be ligatured in place, after being covered with a thin layer of gutta percha. Dr. E. C. Kirk uses for such a purpose surgeon's rubber plaster, carrying it around the tooth. Elastic caps are now made to secure devitalizing mixtures in isolated and fractured teeth.