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 : There was no significant difference between elderly and young volunteers in pupillary response to tropicamide at any time point ( p > 0 . 05 ) .
### Output Text:
RESULTS : There was no significant difference between elderly and young volunteers in pupillary response to <span class="chemical">tropicamide</span> at any time point ( p > 0 . 05 ) . 