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: Since massive albuminuria occurred after 6 days of treatment , the time - course study was divided into two stages : pre - nephrotic stage ( day 1 - 5 ) and nephrotic stage ( day 6 - 11 ) .
### Output Text:
Since massive albuminuria occurred after 6 days of treatment , the time - course study was divided into two stages : pre - nephrotic stage ( day 1 - 5 ) and nephrotic stage ( day 6 - 11 ) . 