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: OBJECTIVE : In this study the effect of glyceryl trinitrate on the prostigmine - morphine - induced sphincter of Oddi spasm was evaluated in nine female patients with sphincter of Oddi dyskinesia .
### Output Text:
OBJECTIVE : In this study the effect of <span class="chemical">glyceryl trinitrate</span> on the <span class="chemical">prostigmine</span> - <span class="chemical">morphine</span> - induced sphincter of Oddi spasm was evaluated in nine female patients with sphincter of Oddi dyskinesia . 