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: This occurred in association with an increase in urinary protein content from 1 . 8 + / - 1 to 99 . 0 + / - 61 mg / day ( p < 0 . 001 ) .
### Output Text:
This occurred in association with an increase in urinary protein content from 1 . 8 + / - 1 to 99 . 0 + / - 61 mg / day ( p < 0 . 001 ) . 