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: On the other hand , enflurane may prove to be a safe fast acting activator of epileptic foci during corticography or depth electrode intraoperative recordings .
### Output Text:
On the other hand , <span class="chemical">enflurane</span> may prove to be a safe fast acting activator of epileptic foci during corticography or depth electrode intraoperative recordings . 