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: A substantial degree of contralateral preference was still evident when amphetamine was administered for the first time 24 days after lesioning , indicating involvement of spared cells in the contralateral rotation .
### Output Text:
A substantial degree of contralateral preference was still evident when <span class="chemical">amphetamine</span> was administered for the first time 24 days after lesioning , indicating involvement of spared cells in the contralateral rotation . 