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: Changes in peroxisomes in preneoplastic liver and hepatoma of mice induced by alpha - benzene hexachloride .
### Output Text:
Changes in peroxisomes in preneoplastic liver and hepatoma of mice induced by <span class="chemical">alpha - benzene hexachloride</span> . 