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
                           1 benzathine benzylpenicillin
                           2.1 benzylpenicillin - C₁₆H₁₈N₂O₄S
                           2.2 benzylpenicillin potassium - C₁₆H₁₇KN₂O₄S
                           2.3 benzylpenicillin sodium - C₁₆H₁₇N₂NaO₄S
                           3.1 phenoxymethylpenicillin - C₁₆H₁₈N₂O₅S
                           3.2 phenoxymethylpenicillin calcium - (C₁₆H₁₇N₂O₅S)₂Ca·2H₂O
                           3.3 phenoxymethylpenicillin potassium - C₁₆H₁₇KN₂O₅S
                           4 procaine benzylpenicillin - C₁₆H₁₈N₂O₄S·C₁₃H₂₀N₂O₂·H₂O