_The Drying Action of Formaldehyde._—Formaldehyde is derived from methyl spirits, which in itself has an active affinity for water. The amount of water ordinarily mixed in formalin in the compounding of a formaldehyde fluid is not sufficient to satisfy the appetite of the formaldehyde for more water. When a formaldehyde fluid comes in contact with moisture laden skin, there will be a movement of moisture from the skin toward the formaldehyde fluid, thereby reducing the degree of moisture in the skin and in that way causing it to become dry. When the skin becomes dry, it changes in color the same as in natural evaporation.
_Treatment._—There are three conditions in the skin met by the operator. The first is where there is a predisposition toward dryness and this is where the skin does not contain a normal amount of moisture to begin with. In old age cases, tubercular, and anemic bodies, the ordinary embalming fluid should be diluted at least one half for the first part of the injection, thus reducing the appetite for moisture on the part of the fluid. In addition to this, water or a face solution should be used externally to prevent outward evaporation from further reducing the moisture in the skin. The fluid exhibits a tendency to draw water into the pores, thus maintaining to a large degree, the normal moisture percentage.
The second condition met with is one in which the skin contains a normal amount of moisture. In this case it would not be necessary to reduce the strength of the standard fluid at any time during the injection, but it is necessary to apply water or a face solution externally to limit outward evaporation and to provide a source whereby moisture could be drawn into the pores by the appetite of the formaldehyde, thus again maintaining the normal percentage of moisture in the skin.
The third condition is one in which the skin along with the balance of the body, will contain more than a normal percentage of moisture. This condition may be looked for in edematous or dropsical cases. The injection in these cases should be normal in strength unless the dropsy is very pronounced, when an overnormal injection can be given without reducing the moisture percentage in the skin below the normal point.