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 morphine - induced hyperactivity was potentiated by scopolamine and attenuated by physostigmine .
### Output Text:
The <span class="chemical">morphine</span> - induced hyperactivity was potentiated by <span class="chemical">scopolamine</span> and attenuated by <span class="chemical">physostigmine</span> . 