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: CONCLUSION : These results provide the first evidence of the effectiveness of glyceryl trinitrate on the morphine - induced sphincter of Oddi spasm in humans .
### Output Text:
CONCLUSION : These results provide the first evidence of the effectiveness of <span class="chemical">glyceryl trinitrate</span> on the <span class="chemical">morphine</span> - induced sphincter of Oddi spasm in humans . 