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: Renal papillary necrosis ( RPN ) and a decreased urinary concentrating ability developed during continuous long - term treatment with aspirin and paracetamol in female Fischer 344 rats .
### Output Text:
Renal papillary necrosis ( RPN ) and a decreased urinary concentrating ability developed during continuous long - term treatment with <span class="chemical">aspirin</span> and <span class="chemical">paracetamol</span> in female Fischer 344 rats . 