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: Clinical and experimental data published to date suggest several possible mechanisms by which cocaine may result in acute myocardial infarction .
### Output Text:
Clinical and experimental data published to date suggest several possible mechanisms by which <span class="chemical">cocaine</span> may result in acute myocardial infarction . 