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: Eight cancer patients in the terminal stages of the disease treated with high doses of intravenous morphine developed hyperalgesia .
### Output Text:
Eight cancer patients in the terminal stages of the disease treated with high doses of intravenous <span class="chemical">morphine</span> developed hyperalgesia . 