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: Similar experiments were conducted in BALB / c mice treated with PJ34 or vehicle .
### Output Text:
Similar experiments were conducted in BALB / c mice treated with <span class="chemical">PJ34</span> or vehicle . 