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 patient received atropine 0 . 5 - 1 mg and chest compressions , before sinus rhythm again took over .
### Output Text:
The patient received <span class="chemical">atropine</span> 0 . 5 - 1 mg and chest compressions , before sinus rhythm again took over . 