Natura - nature actualia - actual entities Mundus Plinius - physical world naturalia - natural bodies "crystal-kingdom" chemical substances chemical compounds Class amides [RkE(=O)l(OH)m (l≠0; ≥1 (OH):=(NR2))] Class primary amides [acyl-NR2] Class lactams [~NRC(=O)[CR2]n~] - cyclic amides of amino carboxylic acids Class β-lactams (4 ring atoms) Class penams Class penicillins procaine benzylpenicillin - C16H18N2O4S·C13H20N2O2·H2O