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: Focal cerebral ischemia in rats : effect of phenylephrine - induced hypertension during reperfusion .
### Output Text:
Focal cerebral ischemia in rats : effect of <span class="chemical">phenylephrine</span> - induced hypertension during reperfusion . 