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 initial dose of amantadine depressed locomotor activity in all mouse strains studied with the BALB / C mice being the most sensitive .
### Output Text:
The initial dose of <span class="chemical">amantadine</span> depressed locomotor activity in all mouse strains studied with the BALB / C mice being the most sensitive . 