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: Randomized , double - blind trial of mazindol in Duchenne dystrophy .
### Output Text:
Randomized , double - blind trial of <span class="chemical">mazindol</span> in Duchenne dystrophy . 