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 conclusion , ouabain - induced mania - like behavior may provide a useful animal model to test the hypothesis of the involvement of oxidative stress in bipolar disorder .
### Output Text:
In conclusion , <span class="chemical">ouabain</span> - induced mania - like behavior may provide a useful animal model to test the hypothesis of the involvement of oxidative stress in bipolar disorder . 