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: Our results confirm the alteration in dynamic response of blood vessels during the change of pressure in gentamicin - treated animals .
### Output Text:
Our results confirm the alteration in dynamic response of blood vessels during the change of pressure in <span class="chemical">gentamicin</span> - treated animals . 