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 following case describes two children acutely poisoned with pemoline who experienced profound choreoathetosis .
### Output Text:
The following case describes two children acutely poisoned with <span class="chemical">pemoline</span> who experienced profound choreoathetosis . 