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 authors examined the anticonvulsant effects of MK - 801 on the pilocarpine - induced seizure model .
### Output Text:
The authors examined the anticonvulsant effects of <span class="chemical">MK - 801</span> on the <span class="chemical">pilocarpine</span> - induced seizure model . 