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: The aims of this study were to confirm our previous findings in a separate cohort of patients and to determine the time course of the cardiovascular consequences of stopping selegiline in the expectation that this might shed light on the mechanisms by which the drug causes orthostatic hypotension .
### Output Text:
The aims of this study were to confirm our previous findings in a separate cohort of patients and to determine the time course of the cardiovascular consequences of stopping <span class="chemical">selegiline</span> in the expectation that this might shed light on the mechanisms by which the drug causes orthostatic hypotension . 