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: Since glyceryl trinitrate is able to overcome even the drastic effect of morphine , it might be of relevance in the treatment of sphincter of Oddi dyskinesia .
### Output Text:
Since <span class="chemical">glyceryl trinitrate</span> is able to overcome even the drastic effect of <span class="chemical">morphine</span> , it might be of relevance in the treatment of sphincter of Oddi dyskinesia . 