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: When instilled directly into the bladder , CAA exerts urotoxic effects , it is , however , susceptible to detoxification with mesna .
### Output Text:
When instilled directly into the bladder , <span class="chemical">CAA</span> exerts urotoxic effects , it is , however , susceptible to detoxification with <span class="chemical">mesna</span> . 