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: Conservative treatment , including bladder irrigation with physiological saline and instillation of prostaglandin F2 alpha , failed to totally control hemorrhage .
### Output Text:
Conservative treatment , including bladder irrigation with physiological saline and instillation of <span class="chemical">prostaglandin F2 alpha</span> , failed to totally control hemorrhage . 