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: Extensive replacement fibrosis ( quantified by Sirius red staining ) developed during the off - dosing period .
### Output Text:
Extensive replacement fibrosis ( quantified by Sirius red staining ) developed during the off - dosing period . 