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 : At 8 weeks , all micturition per day decreased from 16 .
### Output Text:
RESULTS : At 8 weeks , all micturition per day decreased from 16 . 