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: The frequency and predictability of hematuria are not precise , and at least daily monitoring by urine Hematest is essential , adding Mesna to the infusate in patients with persistent hematuria .
### Output Text:
The frequency and predictability of hematuria are not precise , and at least daily monitoring by urine Hematest is essential , adding <span class="chemical">Mesna</span> to the infusate in patients with persistent hematuria . 