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 also reduced the rise in plasma aldosterone and urine potassium excretion following bendrofluazide and increased the urine sodium / potassium ratio .
### Output Text:
<span class="chemical">Timolol</span> also reduced the rise in plasma <span class="chemical">aldosterone</span> and urine <span class="chemical">potassium</span> excretion following <span class="chemical">bendrofluazide</span> and increased the urine <span class="chemical">sodium</span> / <span class="chemical">potassium</span> ratio . 