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: Histology was performed in DOX - rats at 6 and 9 weeks after the last DOX dose and in all controls .
### Output Text:
Histology was performed in <span class="chemical">DOX</span> - rats at 6 and 9 weeks after the last <span class="chemical">DOX</span> dose and in all controls . 