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: Amnesia produced by scopolamine and cycloheximide were reversed by morphine given 30 min before the test trial ( pre - test ) , and pre - test morphine also facilitated the memory retrieval in the animals administered naloxone during the training trial .
### Output Text:
Amnesia produced by <span class="chemical">scopolamine</span> and <span class="chemical">cycloheximide</span> were reversed by <span class="chemical">morphine</span> given 30 min before the test trial ( pre - test ) , and pre - test <span class="chemical">morphine</span> also facilitated the memory retrieval in the animals administered <span class="chemical">naloxone</span> during the training trial . 