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: Conversely , brain normetanephrine concentration was increased from saline control by amantadine in the BALB / C mice .
### Output Text:
Conversely , brain <span class="chemical">normetanephrine</span> concentration was increased from saline control by <span class="chemical">amantadine</span> in the BALB / C mice . 