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: Readministration of amantadine , after a drug - free overnight period , increased motility from respective saline control in all strains with exception of the BALB / C mice where suppression of motility occurred .
### Output Text:
Readministration of <span class="chemical">amantadine</span> , after a drug - free overnight period , increased motility from respective saline control in all strains with exception of the BALB / C mice where suppression of motility occurred . 