Natura - nature actualia - actual entities Mundus Plinius - physical world naturalia - natural bodies "crystal-kingdom" chemical substances chemical compounds Class esters [acyl-XR, etc.; R'kE(=O)l(OH)m (l≠0; ≥1 (OH):=(XR)), etc.; X=O,S,Se,Te,etc.; R≠H] Class glycerides Class triglycerides [RC(=O)OCH2CH(OC(=O)R)CH2OC(=O)R]