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: In Mg ( 2 + ) - free bathing medium containing bicuculline , conditions designed to increase excitability in the slices , electrical stimulation of the hilus resulted in a single population spike in granule cells from control mice and pilocarpine - treated mice that did not experience SE .
### Output Text:
In <span class="chemical">Mg</span> ( 2 + ) - free bathing medium containing <span class="chemical">bicuculline</span> , conditions designed to increase excitability in the slices , electrical stimulation of the hilus resulted in a single population spike in granule cells from control mice and <span class="chemical">pilocarpine</span> - treated mice that did not experience SE . 