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: Five male Wistar rats received repeated subcutaneous PAN injections ; five controls received saline only .
### Output Text:
Five male Wistar rats received repeated subcutaneous <span class="chemical">PAN</span> injections ; five controls received saline only . 