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 effect of long - term timolol treatment on heart size after myocardial infarction was evaluated by X - ray in a double - blind study including 241 patients ( placebo 126 , timolol 115 ) .
### Output Text:
The effect of long - term <span class="chemical">timolol</span> treatment on heart size after myocardial infarction was evaluated by X - ray in a double - blind study including 241 patients ( placebo 126 , <span class="chemical">timolol</span> 115 ) . 