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: Two neonates suffered from generalized seizures during the course of intravenous morphine sulfate for post - operative analgesia .
### Output Text:
Two neonates suffered from generalized seizures during the course of intravenous <span class="chemical">morphine sulfate</span> for post - operative analgesia . 