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: The BALB / C mouse was the most sensitive strain and could serve as the strain of choice for evaluating the side effects of amantadine .
### Output Text:
The BALB / C mouse was the most sensitive strain and could serve as the strain of choice for evaluating the side effects of <span class="chemical">amantadine</span> . 