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: An electron microscope study of the livers of paracetamol - treated rats revealed ultrastructural changes in the hepatocytes that resemble those that result from exposure to a variety of known hepatocarcinogens .
### Output Text:
An electron microscope study of the livers of <span class="chemical">paracetamol</span> - treated rats revealed ultrastructural changes in the hepatocytes that resemble those that result from exposure to a variety of known hepatocarcinogens . 