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: METHOD : All subjects received placebo on Day 1 and haloperidol 2 mg on Days 2 and 25 .
### Output Text:
METHOD : All subjects received placebo on Day 1 and <span class="chemical">haloperidol</span> 2 mg on Days 2 and 25 . 