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 effects of sevoflurane on lidocaine - induced convulsions .
### Output Text:
The effects of <span class="chemical">sevoflurane</span> on <span class="chemical">lidocaine</span> - induced convulsions . 