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: We prospectively evaluated the adverse reactions of apraclonidine in 20 normal volunteers by instilling a single drop of 1 % apraclonidine in their right eyes .
### Output Text:
We prospectively evaluated the adverse reactions of <span class="chemical">apraclonidine</span> in 20 normal volunteers by instilling a single drop of 1 % <span class="chemical">apraclonidine</span> in their right eyes . 