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: PKC - alpha null mice ( PKCa KO ) and strain - matched wild type ( WT ) controls were treated with lithium for 0 , 3 or 5 days .
### Output Text:
PKC - alpha null mice ( PKCa KO ) and strain - matched wild type ( WT ) controls were treated with <span class="chemical">lithium</span> for 0 , 3 or 5 days . 