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: Halogenated anesthetics form liver adducts and antigens that cross - react with halothane - induced antibodies .
### Output Text:
Halogenated anesthetics form liver adducts and antigens that cross - react with <span class="chemical">halothane</span> - induced antibodies . 