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 role of nitric oxide in convulsions induced by lindane in rats .
### Output Text:
The role of <span class="chemical">nitric oxide</span> in convulsions induced by <span class="chemical">lindane</span> in rats . 