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: Male CD - 1 mice were treated with warfarin ( 2 mg / kg over 24 h ) , resulting in a mean ( + / - s . d . ) International Normalized Ratio of 3 . 5 + / - 0 . 9 .
### Output Text:
Male CD - 1 mice were treated with <span class="chemical">warfarin</span> ( 2 mg / kg over 24 h ) , resulting in a mean ( + / - s . d . ) International Normalized Ratio of 3 . 5 + / - 0 . 9 . 