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: No enhancement by phenobarbital of the hepatocarcinogenicity of a choline - devoid diet in the rat .
### Output Text:
No enhancement by <span class="chemical">phenobarbital</span> of the hepatocarcinogenicity of a <span class="chemical">choline</span> - devoid diet in the rat . 