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: The pressure dynamic responses of isolated blood vessels show a faster pressure change in gentamicin - treated animals ( 8 . 07 + / - 1 . 7 s vs . 5 . 64 + / - 0 . 18 s ) .
### Output Text:
The pressure dynamic responses of isolated blood vessels show a faster pressure change in <span class="chemical">gentamicin</span> - treated animals ( 8 . 07 + / - 1 . 7 s vs . 5 . 64 + / - 0 . 18 s ) . 