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: The present study was undertaken to assess lithium - induced polyuria in mice deficient in microsomal prostaglandin E synthase - 1 ( mPGES - 1 ) .
### Output Text:
The present study was undertaken to assess <span class="chemical">lithium</span> - induced polyuria in mice deficient in microsomal <span class="chemical">prostaglandin E</span> synthase - 1 ( mPGES - 1 ) . 