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: Herein , we investigated the behavioral and biochemical effects induced by the ICV administration of ouabain in rats .
### Output Text:
Herein , we investigated the behavioral and biochemical effects induced by the ICV administration of <span class="chemical">ouabain</span> in rats . 