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: Scopolamine was used as a positive control to detect age - dependent changes in central cholinergic functioning in the elderly .
### Output Text:
<span class="chemical">Scopolamine</span> was used as a positive control to detect age - dependent changes in central cholinergic functioning in the elderly . 