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: The timolol - treated patients showed a small but significant increase in heart size from baseline in contrast to a decrease in the placebo group .
### Output Text:
The <span class="chemical">timolol</span> - treated patients showed a small but significant increase in heart size from baseline in contrast to a decrease in the placebo group . 