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: These ecstasy - specific effects may be related to the vulnerability of isocortical and allocortical regions to the neurotoxic effects of ecstasy .
### Output Text:
These <span class="chemical">ecstasy</span> - specific effects may be related to the vulnerability of isocortical and allocortical regions to the neurotoxic effects of <span class="chemical">ecstasy</span> . 