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 39 - year - old woman had spread a warfarin - type rat poison around her house weekly using her bare hands , with no washing post application .
### Output Text:
The 39 - year - old woman had spread a <span class="chemical">warfarin</span> - type rat poison around her house weekly using her bare hands , with no washing post application . 