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 glomerulopathy was induced by seven serial injections of PAN over 12 wk .
### Output Text:
The glomerulopathy was induced by seven serial injections of <span class="chemical">PAN</span> over 12 wk . 