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: Spontaneous renal recovery occurred upon cessation of the slimming pills , but mild interstitial fibrosis and tubular atrophy was still evident histologically 4 months later .
### Output Text:
Spontaneous renal recovery occurred upon cessation of the slimming pills , but mild interstitial fibrosis and tubular atrophy was still evident histologically 4 months later . 