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: Effect of aspirin on N - [ 4 - ( 5 - nitro - 2 - furyl ) - 2 - thiazolyl ] - formamide - induced epithelial proliferation in the urinary bladder and forestomach of the rat .
### Output Text:
Effect of <span class="chemical">aspirin</span> on <span class="chemical">N - [ 4 - ( 5 - nitro - 2 - furyl ) - 2 - thiazolyl ] - formamide</span> - induced epithelial proliferation in the urinary bladder and forestomach of the rat . 