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: Mouse strain - dependent effect of amantadine on motility and brain biogenic amines .
### Output Text:
Mouse strain - dependent effect of <span class="chemical">amantadine</span> on motility and brain biogenic <span class="chemical">amines</span> . 