Diffusion coefficients of salicylic acid (SA) in the vehicles and the skin and partition coefficients of SA between the intact or stripped skin and a saline solution were measured, the simulation of drug absorption from the vehicles, based on the theory in Part II, was carried out, and the proportionalities between the calculated and the experimental absorption values were sufficient for all vehicles. It was found that the skin layer has an unknown nondiffusional resistance by an absorption experiment through the stripped skin. Volume effect of the drug phase on the percent absorption was interpreted by an accumulation of the vehicle at the circumference of the cell caused by an interfacial tension between the vehicle and the cell.
