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: Cocaine , ethanol , and cocaethylene cardiotoxity in an animal model of cocaine and ethanol abuse .
### Output Text:
<span class="chemical">Cocaine</span> , <span class="chemical">ethanol</span> , and <span class="chemical">cocaethylene</span> cardiotoxity in an animal model of cocaine and ethanol abuse . 