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 deformations caused by both coniine and nicotine sulfate were excessive flexion or extension of one or more toes .
### Output Text:
The deformations caused by both <span class="chemical">coniine</span> and <span class="chemical">nicotine</span> sulfate were excessive flexion or extension of one or more toes . 