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: RESULTS : Of the 206 dogs treated with CCNU , 185 met the inclusion criteria for at least one class of toxicity .
### Output Text:
RESULTS : Of the 206 dogs treated with <span class="chemical">CCNU</span> , 185 met the inclusion criteria for at least one class of toxicity . 