Aloe; Drug Carriers; Excipients/pharmacology; Skin Absorption/drug effects; Skin/drug effects; Animals; Caffeine/chemistry; Caffeine/metabolism; Chemistry, Pharmaceutical; Chromatography, High Pressure Liquid/methods; Colchicine/chemistry; Colchicine/metabolism; Diffusion Chambers, Culture; Excipients/chemistry; Excipients/metabolism; Gels; Mandelic Acids/chemistry; Mandelic Acids/metabolism; Mefenamic Acid/chemistry; Mefenamic Acid/metabolism; Molecular Weight; Organ Culture Techniques; Permeability/drug effects; Plant Extracts/pharmacology; Quinine/chemistry; Quinine/metabolism; Skin/metabolism; Solubility; Swine; Time Factors; Water/chemistry