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: RESULTS : Sensitivity to several convulsion endpoints induced by nicotine , carbachol , and neostigmine were significantly greater in WSR versus WSP mice .
### Output Text:
RESULTS : Sensitivity to several convulsion endpoints induced by <span class="chemical">nicotine</span> , <span class="chemical">carbachol</span> , and <span class="chemical">neostigmine</span> were significantly greater in WSR versus WSP mice . 