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: Timolol gellan showed a numerically but not significantly smaller reduction in 24 - hour heart rate , compared with timolol solution .
### Output Text:
<span class="chemical">Timolol</span> gellan showed a numerically but not significantly smaller reduction in 24 - hour heart rate , compared with <span class="chemical">timolol</span> solution . 