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: Urinary volume and serum creatinine levels recovered to the normal range , with urinary protein disappearing completely within 40 days .
### Output Text:
Urinary volume and serum <span class="chemical">creatinine</span> levels recovered to the normal range , with urinary protein disappearing completely within 40 days . 