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: FINDINGS : A temporal relationship was found between topical papaverine and BAEP changes leading to complete waveform loss .
### Output Text:
FINDINGS : A temporal relationship was found between topical <span class="chemical">papaverine</span> and BAEP changes leading to complete waveform loss . 