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: These results suggest that the peak expression of iNOS antigen was followed by that of bFGF antigen , and bFGF may have a suppressive effect on iNOS expression in these rat arteritis models .
### Output Text:
These results suggest that the peak expression of iNOS antigen was followed by that of bFGF antigen , and bFGF may have a suppressive effect on iNOS expression in these rat arteritis models . 