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: Animal model of mania induced by ouabain : Evidence of oxidative stress in submitochondrial particles of the rat brain .
### Output Text:
Animal model of mania induced by <span class="chemical">ouabain</span> : Evidence of oxidative stress in submitochondrial particles of the rat brain . 