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: CONCLUSION : In patients with risk factors , e . g . regular consumption of alcohol , liver failure is possible when therapeutic doses are ingested .
### Output Text:
CONCLUSION : In patients with risk factors , e . g . regular consumption of <span class="chemical">alcohol</span> , liver failure is possible when therapeutic doses are ingested . 