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: DESIGN : A cross - sectional design in stable , treated patients with schizophrenia evaluated using a frequently sampled intravenous glucose tolerance test and the Bergman minimal model analysis .
### Output Text:
DESIGN : A cross - sectional design in stable , treated patients with schizophrenia evaluated using a frequently sampled intravenous <span class="chemical">glucose</span> tolerance test and the Bergman minimal model analysis . 