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: Co - carcinogenic effect of retinyl acetate on forestomach carcinogenesis of male F344 rats induced with butylated hydroxyanisole .
### Output Text:
Co - carcinogenic effect of <span class="chemical">retinyl acetate</span> on forestomach carcinogenesis of male F344 rats induced with <span class="chemical">butylated hydroxyanisole</span> . 