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: Both verapamil ( 10 mg / kg i . p . ) and NH4Ac pretreatment enhanced morphine analgesia - and diazepam - induced muscular incoordination and antagonized amphetamine - induced motor activity , and neither verapamil nor NH4Ac affected the convulsant action of metrazol .
### Output Text:
Both <span class="chemical">verapamil</span> ( 10 mg / kg i . p . ) and <span class="chemical">NH4Ac</span> pretreatment enhanced <span class="chemical">morphine</span> analgesia - and <span class="chemical">diazepam</span> - induced muscular incoordination and antagonized <span class="chemical">amphetamine</span> - induced motor activity , and neither <span class="chemical">verapamil</span> nor <span class="chemical">NH4Ac</span> affected the convulsant action of <span class="chemical">metrazol</span> . 