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: He gave a five - year history of polyuria and polydipsia , during which time urinalysis had been negative for glucose .
### Output Text:
He gave a five - year history of polyuria and polydipsia , during which time urinalysis had been negative for <span class="chemical">glucose</span> . 