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: Venlafaxine is a new antidepressant agent that inhibits the reuptake of serotonin and norepinephrine .
### Output Text:
<span class="chemical">Venlafaxine</span> is a new antidepressant agent that inhibits the reuptake of <span class="chemical">serotonin</span> and <span class="chemical">norepinephrine</span> . 