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 pressure dynamic properties , quantitatively defined by comparative pressure dynamic and total pressure dynamic , confirm the alteration in dynamic response of blood vessels during the change of pressure in gentamicin - treated animals and beneficial effects of vitamin C administration .
### Output Text:
The pressure dynamic properties , quantitatively defined by comparative pressure dynamic and total pressure dynamic , confirm the alteration in dynamic response of blood vessels during the change of pressure in <span class="chemical">gentamicin</span> - treated animals and beneficial effects of <span class="chemical">vitamin C</span> administration . 