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: On the 13th day , antinociceptive effects were assessed using a model of inflammatory nociception , pain - induced functional impairment model , and the charcoal meal test was used to evaluate the intestinal transit .
### Output Text:
On the 13th day , antinociceptive effects were assessed using a model of inflammatory nociception , pain - induced functional impairment model , and the <span class="chemical">charcoal</span> meal test was used to evaluate the intestinal transit . 