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: Does aspirin increase gastrointestinal bleeding or hemorrhagic strokes ?
### Output Text:
Does <span class="chemical">aspirin</span> increase gastrointestinal bleeding or hemorrhagic strokes ? 