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: In vitro , fluoxetine induced pulmonary arterial muscle contraction in fetal , but not adult , animals ( P < 0 . 01 ) and reduced serotonin - induced contraction at both ages ( P < 0 . 01 ) .
### Output Text:
In vitro , <span class="chemical">fluoxetine</span> induced pulmonary arterial muscle contraction in fetal , but not adult , animals ( P < 0 . 01 ) and reduced <span class="chemical">serotonin</span> - induced contraction at both ages ( P < 0 . 01 ) . 