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: CONCLUSION : The present experimental findings substantiate the clinically observed anxiogenic potential of ciprofloxacin and norfloxacin .
### Output Text:
CONCLUSION : The present experimental findings substantiate the clinically observed anxiogenic potential of <span class="chemical">ciprofloxacin</span> and <span class="chemical">norfloxacin</span> . 