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: Five days after the onset of the symptoms of meningitis , the patient aspirated stomach contents and needed endotracheal intubation .
### Output Text:
Five days after the onset of the symptoms of meningitis , the patient aspirated stomach contents and needed endotracheal intubation . 