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: Flurothyl ether produced hypothermia which was correlated with the duration of flurothyl exposure ; however , the relationship of hypothermia to seizure induction was unclear .
### Output Text:
<span class="chemical">Flurothyl</span> <span class="chemical">ether</span> produced hypothermia which was correlated with the duration of <span class="chemical">flurothyl</span> exposure ; however , the relationship of hypothermia to seizure induction was unclear . 