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: METHODS : Thirty - five Wistar rats were given 1 . 5 mg / kg DOX , i . v . , weekly for up to 8 weeks for a total cumulative dose of 12 mg / kg BW .
### Output Text:
METHODS : Thirty - five Wistar rats were given 1 . 5 mg / kg <span class="chemical">DOX</span> , i . v . , weekly for up to 8 weeks for a total cumulative dose of 12 mg / kg BW . 