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: METHODS : Puromycin aminonucleoside ( PAN ) was administered to Sprague Dawley rats to induce proteinuria .
### Output Text:
METHODS : <span class="chemical">Puromycin aminonucleoside</span> ( <span class="chemical">PAN</span> ) was administered to Sprague Dawley rats to induce proteinuria . 