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: Subsequent amantadine treatments produced enhancement of motility from corresponding control in all mouse strains with the BALB / C mice being the least sensitive .
### Output Text:
Subsequent <span class="chemical">amantadine</span> treatments produced enhancement of motility from corresponding control in all mouse strains with the BALB / C mice being the least sensitive . 