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: The association of cocaine and amphetamine use with hemorrhagic and ischemic stroke is based almost solely on data from case series .
### Output Text:
The association of <span class="chemical">cocaine</span> and <span class="chemical">amphetamine</span> use with hemorrhagic and ischemic stroke is based almost solely on data from case series . 