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: A muscarinic receptor blocker , atropine , disrupted haloperidol - induced catalepsy .
### Output Text:
A muscarinic receptor blocker , <span class="chemical">atropine</span> , disrupted <span class="chemical">haloperidol</span> - induced catalepsy . 