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: Lithium induced nephrogenic diabetes insipidus is considered to be reversible on cessation of therapy but polyuria persisted in this patient for ten years after lithium was stopped .
### Output Text:
<span class="chemical">Lithium</span> induced nephrogenic diabetes insipidus is considered to be reversible on cessation of therapy but polyuria persisted in this patient for ten years after <span class="chemical">lithium</span> was stopped . 