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: In patients with schizophrenia , ketamine exacerbates the core symptoms of illness , supporting the hypothesis of a glutamatergic dysfunction .
### Output Text:
In patients with schizophrenia , <span class="chemical">ketamine</span> exacerbates the core symptoms of illness , supporting the hypothesis of a glutamatergic dysfunction . 