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: Effect of glyceryl trinitrate on the sphincter of Oddi spasm evoked by prostigmine - morphine administration .
### Output Text:
Effect of <span class="chemical">glyceryl trinitrate</span> on the sphincter of Oddi spasm evoked by <span class="chemical">prostigmine</span> - <span class="chemical">morphine</span> administration . 