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: cTnT found in rats after 12 mg / kg were significantly greater than that found after 7 . 5 mg / kg DOX .
### Output Text:
cTnT found in rats after 12 mg / kg were significantly greater than that found after 7 . 5 mg / kg <span class="chemical">DOX</span> . 