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: Although certain clinical and experimental findings support the hypothesis that spasm involves the epicardial , medium - size vessels , other data suggest intramural vasoconstriction .
### Output Text:
Although certain clinical and experimental findings support the hypothesis that spasm involves the epicardial , medium - size vessels , other data suggest intramural vasoconstriction . 