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: Fatal excited delirium following cocaine use : epidemiologic findings provide new evidence for mechanisms of cocaine toxicity .
### Output Text:
Fatal excited delirium following <span class="chemical">cocaine</span> use : epidemiologic findings provide new evidence for mechanisms of <span class="chemical">cocaine</span> toxicity . 