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: METHODS : Male Wistar rats ( 150 - 200 g ; 6 rats per group ) were treated with saline or mesna 5 min ( i . p . ) before and 2 and 6 h after ( v . o . ) administration of IFS .
### Output Text:
METHODS : Male Wistar rats ( 150 - 200 g ; 6 rats per group ) were treated with saline or <span class="chemical">mesna</span> 5 min ( i . p . ) before and 2 and 6 h after ( v . o . ) administration of <span class="chemical">IFS</span> . 