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: RESULTS : Both timolol solution and timolol gellan reduced the mean 24 - hour heart rate compared with placebo ( P < or = . 001 ) , and this reduction was most pronounced during the daytime ( - 7 . 5 % change in mean heart rate , - 5 . 7 beats / min ) .
### Output Text:
RESULTS : Both <span class="chemical">timolol</span> solution and <span class="chemical">timolol</span> gellan reduced the mean 24 - hour heart rate compared with placebo ( P < or = . 001 ) , and this reduction was most pronounced during the daytime ( - 7 . 5 % change in mean heart rate , - 5 . 7 beats / min ) . 