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: In order to clarify the nature of this initial contralateral rotation we examined the effect of the duration of recovery period after the lesion , on amphetamine - induced rotational behavior .
### Output Text:
In order to clarify the nature of this initial contralateral rotation we examined the effect of the duration of recovery period after the lesion , on <span class="chemical">amphetamine</span> - induced rotational behavior . 