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: He was found to have atypical plasma cholinesterase with a dibucaine number of 12 , indicating homozygocity .
### Output Text:
He was found to have atypical plasma cholinesterase with a <span class="chemical">dibucaine</span> number of 12 , indicating homozygocity . 