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: Puromycin aminonucleoside nephrosis was induced by single intraperitoneal injection of puromycin aminonucleoside ( PAN , 20 mg / 100g BW ) .
### Output Text:
<span class="chemical">Puromycin aminonucleoside</span> nephrosis was induced by single intraperitoneal injection of <span class="chemical">puromycin aminonucleoside</span> ( <span class="chemical">PAN</span> , 20 mg / 100g BW ) . 