In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The minimum effective plasma concentrations of ( + ) - cibenzoline for digitalis - and adrenaline - induced arrhythmias were 1 . 4 + / - 0 . 4 and 2 . 0 + / - 0 . 6 micrograms / ml , respectively ( mean + / - SD , n = 6 ) .
### Output Text:
The minimum effective plasma concentrations of ( + ) - <span class="chemical">cibenzoline</span> for <span class="chemical">digitalis</span> - and <span class="chemical">adrenaline</span> - induced arrhythmias were 1 . 4 + / - 0 . 4 and 2 . 0 + / - 0 . 6 micrograms / ml , respectively ( mean + / - SD , n = 6 ) . 