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: Thirty minutes after these injections , all mice received lidocaine ( 50 mg / kg , i . p . ) .
### Output Text:
Thirty minutes after these injections , all mice received <span class="chemical">lidocaine</span> ( 50 mg / kg , i . p . ) . 