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: Quinacrine hydrochloride is toxic for the heart of F - 344 rats .
### Output Text:
<span class="chemical">Quinacrine hydrochloride</span> is toxic for the heart of F - 344 rats . 