A ballistometer for the study of the plasto-elastic properties of skin.

The ballistrometer is based on the "drop impact" of a body onto a stationary surface. A collision in one dimension is provoked by allowing a hard body to drop from a given height onto the skin surface to be tested. After the collision, the impacting body undergoes a variable number of rebounds decreasing in amplitude. By measuring the height of the rebounds, the amount of energy returned by the tissue is calculated in terms of coefficient of restitution e. The equipment, consisting of a hammer unit, a feeder-amplifier, and a plotter, is described. Ballistometry has been carried out on skin areas of 46 normal subjects ranging in age from 8 to 80 years, as well as on pathologic and cadaveric skin. The results show a progressive decrease of e with advancing age, as well as differences related to various skin regions. The tests performed on pathologic skin showed a lowered e in epidermal hyperplasia, hyperkeratosis, sclerosis, and dermal infiltration. An increase of e was observed when a high water content was present in the skin.